Does sound alot like low blood pressure at first thought. But it's the type of symptoms that could be a number of things.
Could it be linked to whatever contraception you may use or any other girly problems, my mate got terrible sickness and general feeling 'funny' symptoms with both th injection and the types of pill she tried. Just something to think about.
It could just be a lack of sleep...even too much sleep, or simply not enough fuel from skipping breakfasts. Hopefuly your doc' can get some answers.
My dads currently having tests for something pretty much the same, and it's just annoying because one set of tests have shown 'nothihng' to be wrong and we're waiting for the others. But being told there is nothing wrong when something clearly is, is just frustrating.
Let us know how you go
