I fainted quite a lot at one point. Turns out I had a heart condition that meant when getting up from crouching, the heart didn't pump fast enough to get blood up to my brain so I keeled over. It's always worth getting these things checked out!
My first faint was when I was 11. I remember it vividly because I came over all clammy and couldn't go into church with the rest of the choir for evening service. I went home and was 'resting' on the couch watching 'Thunderball' starring Sean Connery. I took one look at that hairy chest and the pattern of my life was set.