fainting

i went to give blood yesterday. i'm not sure what the hell happened but after it was all done, i fainted. bit of a shock - i mean, i've given blood at least a dozen times and nothing's ever happened. i started feeling all weak and faint but thought it would pass and next thing i know, i must have passed out cos i don't remember much until some seemingly very far away shouting which i couldn't make sense of - they were trying to get me back to a horizontal position - and finally understanding they wanted me to take my glasses off but i couldn't. they did it for me and sprayed water mist onto my face, which got me back to reality. but it took another half hour before i got out of my seat. the doctor came to see me and i was given more water, biscuits and fruit paste. then they had a man walk me to the food room - in France, you get an entire meal after giving blood. in the end, it was another 15 mns before i felt good enough to walk the 300m to my place...