Low blood pressure (hypotension) can commonly be caused by dehydration - not enough fluid intake, or losing too much fluid through vomitting or diarrhea. It can also be caused by certain medications. Orthostatic hypotension is also fairly common (I ve had it myself occasionally), which is the low blood pressure which occurs when you ve been lying down or sitting and then suddenly stand up, making you feel really dizzy for a few seconds. So stay hydrated - keep the fluids up - for a start. If it s really bothering you, getting your blood pressure checked by your doctor is quick, simple and painless!