Sounds like low blood pressure, maybe orthostatic hypotension. Try to get your BP checked and in the meantime be really careful changing positions. I spent my entire career bugging people about this yet didn't do it myself when I was having really low BPs from a med combinatio. I knew it and didn't. I fell and tore 3 ligaments on one side, 2 tendons on the same side, my achilles and a ligament on the inside of the ankle. It led to major surgery and 6 weeks of bedrest while I kept my cast up in the air. So learn from me: Also get yourself adjusted before changing position and don't jump up an take off running without knowing if you are strudy!