I use to get that when I was dieting and lost too much weight which caused my blood pressure to be much too low, but then high blood pressure can make a person feel that way.
My doc also told me if a person is slightly dehydrated that could happen too. Low or high blood sugar can make that happen, so many things can be possible.
To play it safe, see your doc. maybe it is anxiety, and/or some other physical condition, but please have it checked.
I know what you mentioned is scary. Another thing I forgot, have you checked your meds (if you take any I do not know) if they have side effects like that? Check that out too.
Diuretics, blood pressure meds, AD's, and if a diabetic, insulin dose may be too high or low.
Oh, I know, just so many things today that can cause this sensation
Please take care now,

DE