IWasFirstClarinet
Happens to me in my late 80s when I sit up from the bed. If I sit still for several seconds on the edge of the bed it stops. My doctor said in my case it is merely your blood pressure adjusting and is not a cause for concern. Just sit! So I do.
I do that thing where you hold your finger in front of you and then lift your head up and down, side to side while focusing on the finger.


