There can be many reasons for low blood pressure , such as a result of a fever , alcohol related , being on blood pressure tablets which can slow down your heart rate or taking diuretic tablets which can lead to a drop in blood pressure due to excessive loss of fluid. There is also a pregnancy related condition called hypotension which is the opposite of hypertension (high blood pressure) and is usually nothing to worry about. The best person to ask about this would naturally be your GP. Don't be afraid to voice your concerns as that is what they are there for and will undoubtedly be only too happy to help - rather than having you worry yourself sick.