I'm just an EMT, so take my advice with a grain of salt...and other real medical professionals feel free to correct me if i'm wrong..
mammo is right...the biggest cause is low fluids/dehydration. If you can drink a bunch of water or diluted gatorade (1/2 ade 1/2 water) for an hour or two, the problem could lie elsewhere.
Medications can play tricks with your blood pressure as well...specifically nitro based medications (stuff people take for heart issues)...that's why they say 'if you take nitrates for pain...viagra is not for you)...because viagra & nitro both cause your BP to drop...
The biggest thing is if you feel dizzy to sit/lie down. With low BP...the biggest threat might be fainting, and banging your head on something...
Also...as long as your BP stays above 80, you'll be ok. An easy way to check this is to check your pulse at your wrist. As long as you can feel your pulse...you're above 80.
I would have to agree here. Why not get checked out by your doctor. Plus, where did you get your reading? Blood pressure also fluctuates all the time during the day. My wife's is very low and the doctor loves that fact. Are you experiencing other symptoms with your bp? If not, you may just have lower bp than most, which may not be a bad thing in my opinion, but your doctor can defintely tell you this and explain the situation.
Low blood pressure can be caused by many things, it's best to get a thorough check-up by your doctor to determine why yours is low. The simplest is dehydration, but there are so many that only your doctor will be able to answer this for you. Take care~~~