What I’m trying to determine is if you are doing an inversion practice at all on your own. It is possible, and I want to stress “possible” that what you are feeling is the normal sensations of going upside against gravity.
However, if you’ve been doing a practice for 4 years consistently and you are doing the poses you mention, AND you are having these sensations still then we must rule out what I have stated in the previous paragraph.
Are you checked regularly by your general pracitioner? My next thought would be one of blood pressure. I must assume since you did not mention high or low blood pressure that you have a normal blood pressure as far as you know. Then the only question would be when did you last have a BP check.
An additional posssibility is that you are folding the neck as you mention in the second scenario you illustrate. Many practitioners tend to discount the length in the cervical spine (neck) when they are “busy” lengthening the rest of it. An example would be the student who tosses their head back in a pose like cobra (bhujangasana- boo-jahng-ah-suh-nuh) well before they have learned to drawn the spine in toward the front body in the pose. Mostly they do this becasue they’ve seen it in Yoga Journal or on a DVD. It is meant to be done that way but in integrity with the rest of the human architecture.
But I ramble…point is in forward bending (uttanasana) the crown of the head should point toward the earth unless you are nursing a neck injury. Think about keeping the neck in integrity with the rest of the spine. Also try micro-bending the knees in these forward bends and see if that is at all relieving. It might be beneficial for a qualified teacher to see your posture and make a determination as to your cervical curvature.
Finally, UCSIYP - Use common sense in yoga practice. If you are disquited by the actions in the poses mentioned then do not do them.
