You know Linda, I had a spell for about a year where I would faint at the drop of a hat. They did every test they could, testing my blood for everything, physicals, heart monitoring, etc. They never found out what it was but it left as quick as it came BUT I still have those times when I feel I'm going to faint but I can usually stop it if I'm somewhere that I can lie on my left side in a cool place.
I was boderline anemic and was under tons of stress at the time so they just kind of chalked it up to that.

My very first date with my exhusband we were out eating at a resturant, I started feeling faint and I said I don't feel so good. He said just say WHEN if you want to leave, right off I said WHEN,  I got up and the next thing I know I'm on the floor with the EMT's there asking him "Is she taking any drugs" He was like "I don't know this is our first date I really don't know her that well".. LOL It was funny, we never ever forget that first date.. 

I hope you find out what it is but I sure never knew what caused it for me and like I said it still happens from time to time for no apparent reason????