lightheadedness , sudden low blood pressure

I have had several symptoms for a number of days now. It started with a fairly severe headache that was located behind my eyes, a couple days later I experienced pain in my neck and upper shoulders. This evening at work everytime I would bend over and stand back up my head would feel like it was spinning and I would be mildly nauseated. When I got home from work I checked my blood pressure and it was 100 over 66 while I was sitting up it normally runs 120 to 125 over 70 to 75. Could you possibly give me some idea what is wrong with me.