What Causes Fainting Along With Vomiting And Tremors In The Legs?

Symptoms for an 88 year old female - for years she has suffered fainting spells when sitting down and standing up. Use to be about every six months or longer, now once a week. Here is what else she experiences at about same time - throwing up, feeling weird in her head, face turns red, blood pressure seems to change by going up and down, during this her legs shake. Her blood pressure has run below normal her adult life, in fact when she had surgery years ago they were concerned it had fallen so much they had a hard time of getting it back up. During the last month when fainting has become worse her blood pressure has been extreme like 222 over 94 and another time in the last 2 weeks it was 106 over 43. She is wearing a heart monitor and is taking medicine regulating for atrial fibulation (first tried beta blocker then switched) and a blood thinner. She did not seem to have atrial fibulation attack this morning when she fainted again (checked monitor information). The Drs. seem puzzled.