Thank you for the new pictures in your profile I can see that you have done a very nice job of removing the Lingual frenulum from your picture of being in Kechari.
This certainly shows you have the dedication and are reporting your findings from experience, which sadly is lacking here and on other forums as well.
There is allot of mind scatter and opinions but very little real experience being shared.
I salute you. People reading these forums could do far worse than to listen to that which you report from actual experience. One thing is for certain between my sharing the Kechari experience by not cutting the frenulum using Talabya Kriya only ( FYI this does not involve sawing the tongue on the teeth. ) and your removal people are going to learn more about Kechari than has ever been publicly shared before.
To answer your question about being sure if it is an energetic experience versus Vacuum I will attempt to do my best below.
Please excuse the analogy but there is no other way I can think of that accurately describes the energetic demands the tongue experiences in sadhana how it feels other than by comparison with anatomy all men share in common.
It occurs the same may be true of women & their anatomy but not having the anatomy I can not say.
To the person reading this I write try your best to really read what is being written so you can comprehend if you just give this a casual once over you are likely to upset yourself and miss the meaning.
The best analogy I can give is that of a Penis that has become not only erect but there is a desire for it to be used for it's reproductive function.
Now all men know there is erect and then there is really, really, really erect.
One female may have what it takes to get the parts in gear and ready to work but the female that really turns you on makes all the difference.
The penis will be extra excited the erection longer and harder and the energetic conductivity very present and impossible to ignore and one will most definitely feel strong pulsation and vibration from the front Kshetram of the second Chakra Swadisthana into and along and through the organ of reproduction.
Now this is what it feels like in the tongue in Kechari but here are the big, big big differences.
1. In the first example the flavor, vibratory rate essence is mostly second Chakra with 1st and third blended to a lesser extent and is well fluidity like in nature it is not a very highly vibratory state at all it is rather slow pulsing in large waves that build and that crash and recede in oscillation by comparison with the energy that is manifested in the centers as one goes upwards. As one goes upwards the wavelengths shorten considerably and there the peaks and valleys are much closer together giving the impression of greater speed.
2. Kriya Practice as is traditionally taught by the Lahiri Mahasaya lineage purposely engages all the centers from bottom to top and top to bottom creating the movement in sushumna from the practice and the energetic conductivity I encounter in the spine and the tongue in Kechari. I may not speak for another persons practice from a different school as it is different and as should be expected there are differences in experience.
3. The quality of the energy encountered in Kechari is that of all of the centers below Ajna melded together and seeking upward union in Ajna and Sahasrara first it is from lower to Ajna then even Ajna blends to go to Sahasrara and feed the desire for union between the two poles of Sushumna.
So sexual energy which causes a certain energetic yearning is of 1 or all 3 of the lower located centers but expressed through the front Kshetram of Swadisthana center and is thusly felt when the conditions are correct and union is being made then released.
The type of union that occurs in Kechari is only similar in that the tongue takes on a similar impossibly energetic yearning to that of a highly aroused penis being enervated primarily from the sex center itself as happens when the excitement is right from the right conditions being met.
The feeling in the tongue is not like what a man feels in the sex organ let me be clear on this point.
What I am trying to describe is the yearning the aching the desire that it be sheathed to the hilt it has for connection the vibratory rates.
The tongue is a conduit at this point there is tremendous unfulfilled desire in it to connect Muladhara to Sahasrara to do its job to complete the circuit and this desire does not subside until it is sheathed in the skull and completes this connection to the best of its ability.
Once this happens it feels at home like ah this is where it belongs not down below with the sharp rocks called teeth Ugh!! how repulsive, tongue being in the mouth is repulsive that is the new feeling mind gets. Strange but true.
I keep writing tongue so people understand but now I am telling all that the tongue stops being the tongue as the subtle body demands this connection the tongue is the switch the connecting draw bridge piece of sushumna.
The tongue now is no longer recognized as just the thing that tastes food as the disgusting mess is smeared all over it. It is viewed, felt experienced as sushumna when in place.
The awareness one has is different and that is the point I am attempting to make above. This awareness becomes identified with the subtle body and knows the physical body exists but is not enamored of it any way. The positions become juxtaposed the subtle body takes on the position of not only preferred reality but the more enduring and real.
From this awareness understands this too is impermanent and continues on.
So the tongue is in Kechari, work has been performed in Sahasrara the entire spine has passed through the humming vibratory states brought on by the Chakras harmoniously expressing together OM is heard and a vibration from these energy centers after piercing the bindu in each and having become internalized in the sushumna.
At this point Kriya Pranayama's are being performed first with the breath and placing OM Japa in the centers, Later the same work is performed in the still state of breath when it occurs on it's own and this is true Pranayama.
When Ajna is reached at the medulla point and the reflection seen in Kutastha there is a very strong energy blossom that occurs here that has already occured on all the centers below it and that energy is taken up in the center of the spine and brought here where all 5 qualities are united this causes the tongue to dive as deeply as it may in ecstatic ecstasy the eyes become rooted on the root of the nose. The tongue is no longer the tongue it is sushumnas missing piece and now things are being made whole again.
From this the light of Kutastha is experienced and sounds are no longer heard all senses are internalized there is a strong connection made to sahasrara all energy seeks to go there from the perineum up up up in the middle of sushumna there is a strong desire at the top of the head that must be fed.
When the breathless states or state of stilled breath occurs then the Kriyas are performed with true pranayama which is moving the attention exactly the way it was moved with the breath. The experience is much different the feeling is of being in a very narrow tunnel thread like it is so thin.
Then in the after-poise state of Kriya the The tongue takes on the vibration of purist serenity and it is the connecting link to Sahasrara it lies against the throat wall pointing straight up and is forgotten as higher states of being are experienced that words can not describe.
As for the Vacuum you describe yes this can be present or not and can aid in keeping the tongue in place during the initial placement of the tongue but the tongue soon grows used to it position and relaxes as if at home after a long days work until the energy is moved then it reacts like water bieng turned on in a hose.
When the desire is present and strong the tongue fills areas in the skull it normally can not when it is first inserted. so the sequence goes like this.
1.Talavia Kriya is practiced this generates saliva and cleanses the pallet and the tongue as well as warms up the tissues.
- Placing Om Japa in the centers is practiced it is during this time that the energetic reaction of the centers begins harmonizing as each lamp lights and vibrates at its specific frequency the spine begins to take up the vibration of the centers and starts to magnetize. The Bindu of each center is pierced by placing OM Japa into the chakra from the rear Kshtram and entry into sushumna begins from C1 to C6 at Medulla and each one in-between the vibratory frequencies felt are the awareness traveling the bindu into sushumna.
3.Once the sushumna has been entered from the rear kshetrams via technique and the conditions met the tongue lays against the back wall of the throat this is caused by energetic desire I have tried to explain the soft pallet opens a small hole for the tip of the tongue when they touch the first waves of ecstasy are experienced this is from the Talu Chakra located at the end of the hard pallet.
4.I stay here and witness that which occurs staying out of my own way trying to just let go and experience rather than allow the shock to make the body tense.
- The desire the ecstasy continues to build all of the first 6 main Chakras and Talu are harmonizing OM is heard,
6.There is a feeling of strong magnetics and vibration in the upper centers of Bindu and Sahasrara and Kutastha but it is separate and not seperate at the same time.
7.There is a strong desire for the tongue to penetrate and become sheathed in the skull.
The tongue slides very nicely into place and a circuit is closed like throwing an electrical switch there is a surge as the lower portion of Sushumna is cleanly connected to the higher portion of Sushumna from here the mind can become stunned by the completion of the vibratory frequencies all culminating and combining in the desire at the top of the head the breathless state occurs the still state of breath occurs this I subsides.
The return: When this high state begins to subside and mind again is operable it is not the same awareness state or mind I first sat down with. The spine is cleanly flowing force now the tube is open. This is opening the knot at Medulla or the knot of the tongue.
Now begins Mahamudra at times the still breath occurs in hitching stops I attempt to inhale but the prana takes over and satisfaction is only known by following the pranic desire to not inhale or if it is on an exhalation exhale any further. This is opening the knot of the Heart & Muladhara. Spontaneous eruptions of energy are felt in the medulla and from Anahata center the same occurs less frequently at Muladhara. Primarily between Anahata and Medulla.
Navi Kriya is practiced which Focuses on loosening the knot at Manipura here the still breath occurs most readily as the blending of airs occur. Note:When the still breath occurs mind and awareness become much different, even more still. Here great energy is felt at the rear Kshetram of Manipura nad Medulla /Kutastha there is a line in sushumna clearly felt connecting the two.
Kriya Pranayama proper which has been described above
13.Yoni Mudra Where the ring and the orb with the star are seen and entered see my Jyoti picture album. http://www.yogaforums.com/forums/members/18916-albums137.html
The after poise state of Kriya.
In every Kriya the tongue is in Kechari and completes the two pieces to make the sushumna whole. If the tongue is removed it will automatically return on its own some times flipping up into place swiftly like a dolphin jumping and flipping up out of the water.
Every Kriya builds on the work of the last and one continues to enter into states of awareness that are further and further than away from where one was when they first sat.
Tongue in Kechari via energetic demand for sushumna to be made whole is the desire felt.
I hope this answers the question completely. I prefer to answer in an experiential way but to do so requires answering as I practice and this means Kriya techniques are the ones used that aid in making the transition from the gross to the subtle body and states that go beyond both.
So this is how Kechari works with me Kriya first required otherwise there is no reason to experience Kechari in it's operational mode.
The exception is if I take a break from Kriya practice then the energies in the body do build up and will cause the connection to occur as the centers become enervated on their own and do as I have described when placing OM Japa in the centers to enter their respective bindu and sushumna.