Dehydration or unusual thirst
However, low blood pressure is not always caused by dehydration, but Dehydration can sometimes reduce your blood pressure. Diuretic overuse, vomiting, fever, severe diarrhea and exercises can all cause dehydration and can potentially be severe if your body loses more water than you are taking. Even mild dehydration( loss 1- 2% of the weight of the body) may result in faintness, swelling and fatigue.