“How you feel Kundalini?”
First, it is important to be able to discriminate between what is just your own imagination, and what is an authentic experience of awakening the kundalini. That is why it is absolutely essential in the practice of, not just kundalini yoga, but any form of yoga - that one brings into one’s experience a quality of remaining an observer which is capable of witnessing from moment to moment whatever arises in your experience - without liking or disliking, without attraction towards or aversion from. If you cannot even be aware of your own mental projections as they arise, then there is very little possibility of awakening enough clarity to be capable of discriminating what is just your imagination and the reality.
As far as experience is concerned, there are many different manifestations of the Kundalini. It will express itself in different ways depending on which aspect of your own life energies are being charged by it. Just as there is electricity, magnetism, electromagnetism, gravity, and so on - similarly at the subtle level there are a variety of different subtle energies which are of different qualities. In the yogic sciences, we refer to them collectively as prana - but it should not be misunderstood that prana just expresses itself in one way. Depending on which part of the body you are considering, there are different aspects of subtle energy which are functioning there. Through each of the chakras, there is a particular form of life energy, each of which is functioning at a certain rate of vibration.
So there are two aspects to understand about the anatomy of the subtle body - one is the vessel which carries energy (nadis), the second is the energy itself which flows through the nadis. It is just like a wire, and the electricity which is flowing behind it. That is in fact what these “chakras” are, they are just a collection of nadis which come together to form a bundle of nadis which carry particular forms of life energy.
Prana is at the level of the heart, udana is at the level of the throat, samana is at the level of the navel, apana is at the sacral level, vyana pervades the whole body, kurmana which assists the opening and closing of the eyes, kirkala at the stomach which assists digestion and also produces the sensation of hunger, and dhananjaya which does not leave the body after death. This is the reason why the body of parahamsa yogananda and several other yogis have taken a much longer time than ordinary to decay - in the case of yogananda it took more than 21 days to start witnessing the effects of bodily decay. This is because the dhananjaya in his system was rich in vitality which helped preserve the body. There are various other subtle energies, but these are just a few.
Depending on which form of energy is more dominant at the time of awakening the Kundalini, it is going to express itself differently. Sometimes, it is in the form of intense heat - sometimes the opposite. Sometimes, it will jump spontaneously from one part of the body to the other - usually in a vertical direction, sometimes it will move gradually like a current of electricity along the spinal cord. Depending on it’s movements, in the yogic sciences we have described the expressions of Kundalini as similar to the movements of different animals. There is that kind of awakening which is of an ant-like movement, there is that kind of awakenign which is a serpent-like movement, there is that kind of awakening which is a bird-like movement, and like this there are various different ways to describe the possibilities of how Kundalini can move in your system. But it is of my own experience that the most common expression of it is a certain current of energy with waves of vibration moving along the spinal cord, sometimes cold and sometimes hot, sometimes pleasant and sometimes unpleasant. It is often unpleasant and even painful if you have not already undergone a thorough purification of the nadis. Because otherwise, if you happen to awaken Kundalini, once it starts rising up the spinal cord, if your nadis have not been purified and the “knots” of energy untied, then it will simply burn it’s way through the nadis by force. If it forces it’s way with too much intensity, it can create several problems in your nervous system as well as psychological disturbances. This is usually what creates the great danger of awakening Kundalini without the proper understanding or without the help of a master, because if you manage to awaken the Kundalini at a time when your system has not yet become prepared to receive it, it may cause more damage than good.