For a couple of years now, I've noticed something strange. I'll be sitting or lying down for awhile, studying or sleeping or some such. Then I'll stand up quickly, clasp my hands above my head, take a deep breath and hold it, and stretch. Sometimes nothing happens, but more and more in the past few years I get slightly dizzy, and my eyes sort of "cloud over" (that's the only way I know how to put it); stuff gets gray and I have to really concentrate hard to clear it. Those last about 3 seconds. It's just a normal thing to me, but sometimes it's much worse. Everything; hearing, feeling, sight, just fades away and it takes all the concentration I have to just be able to keep my feet because of the dizziness. During one of those I also shake really hard. Those last for about 5-7 seconds. The bad one hasn't happened in about 1-1/2 years, but it happened again today and has me worried. I think it may be the holding my breath while I stretch as well as the quick transition from low elevation to high elevation, and it is worse when I'm overtired, but is this normal? Note: This doesn't happen when I just stretch, when I just stand up, or when I just hold my breath. It's the combination of the 3 that brings it on.