Fainting when stretching

I am not sure what category this goes in exactly; I chose the one I thought was best...

I have times where I am very relaxed while sitting, and before I decide to get up, I will stretch very hard, and hold it, but...

Sometimes, in the process of doing so, I first lose my hearing, then I stop seeing colors, then everything fades away in a donut with a shrinking hole, then I pass out.  It doesn't (usually) last for more than a few seconds (although I can't tell I am out in reality), but upon "coming back," the reverse happens, only faster (gain sight back, then colors, then hearing, but I am usually moving back and fourth without knowing I am (like stumbling when you are dizzy) until my head stops throbbing.  I also feel like there is a thump in my head (the throb), probably in the rhythm of my heart.

I tell this to people, and they all just think I am nuts.  But I know what I am feeling.

But I don't know what it is.

[painkiller99]

Do you suffer from hypertension? Do you also experience this when you exert yourself? It would be advisable to consult a neurologist regarding your condition as it may be an early symptom of an underlying cerebrovascular disease.

[digikey]

Last time I had it checked, I had a blood pressure that people would kill for (it is almost perfect).  And, if by exerting you mean the tense feeling you get in your head when you are, say, lifting something heavy, I sometimes do this a little bit when I stretch, but when I am lifting that heavy object when I am not relaxed, I don't have that problem.  It only occurs when I am going from a relaxed to a more awake state.  (like daydreaming kind of relaxed, and lower states of consciousness).

It is very similar to sitting down for a while and then quickly getting up, but with the added throbbing in the back of the head.

Speaking of which, if I remember correctly, I feel it in the back left part of my head, where I have had other problems that people think I am nuts about.  Although it doesn't happen every time I perform one of the following actions, I notice that I get what feels like a "pop" or a "smack" inside my head after I do these things: Make a sudden movement, making a hard landing (like falling on my bottom on the pavement), and even sometimes, just turning my head, although the last one is more rare.  This sensation I have had since as far back as I can remember, but, with the exception of the two people I know who experience the same thing, one of whom is my brother, no one understands what I am talking about.

Note that I am not sure if that is where I feel my head pulse for sure, because as I recover from fainting, I have a sensation of "I am here," but the rest of my senses aren't fully back yet when I seem to feel it.

Also, cerebrovascular, by its roots, would refer to the blood vessels in your cerebrum, right? Where is the cerebrum?  That is all I forgot.

[painkiller99]

Cerebrum = brain.

I noted that you mentioned "similar to sitting down for a while and then quickly getting up".  Does your fainting spells occur when you do this? If yes, you may have orthostatic hypotension.

Orthostatic hypotension can be caused by hypovolemia or can be associated with some conditions such as diabetes or some neurological diseases.  Consult a physician to have your symptoms properly assessed.