I get dizzy if I stand up to fast (common among endurence athletes from what I hear)!
Only injuries I have had was the ones that got me into the sport...I had condramalasia(sp?) and tendenitis in my knees when I used to just run. That got me into cycling which got me into duathlon (run-bike-run) which got me into triathlon. I've had back inuries but not because of training. I've become pretty in tune with my body and know when its time to ease up. Plus I do a lot of preventive maintainence...icing, stretching, and anti-inflamatories.
I think my drive comes from wanting to see how far I can go and push myself...plus a "bit" of competitiveness (maybe a bit masocistic also )!
I don't take my health for granted...I am very thankfull to be able to do what I do.