Originally Posted by mrsD

Welcome to NeuroTalk:

This can be many things, so I think you should see a doctor.

1) low potassium
2) orthostatic hypotension or sudden low blood pressure when bending over or standing up suddenly
3) POTS (does your heart beat really fast when this happens?)
4) Low blood sugar spells
5) reactions to various drugs
6) some form of epilepsy

So really you should see a doctor and get evaluated IMO.
Good luck to you!