My grandmother use to pass out and the doctors had no answer, until she pass out one day and they ran tests immediately. While it was happening. She had a blood clot in the back of the neck. They treated her with dilantin and phenabarbatol (not sure of the spelling). After a couple of times of adjusting her medications, she was fine. Went back to having a normal life. Ask your doctor about blood clots in the back of the neck or to the brain. Good Luck!