Similar to JoshB, one of the things I kept thinking was, 'my life is starting now'.
I felt like I was finally being *born*, weird as it sounds. As far as fears go, I was kind of dreading acne and baldness; the acne I knew would happen (I've always been acne prone to start with) so it was less of an 'oh no this might happen' and more of a '->-bleeped-<-, this is going to happen, gonna have to suck it up and deal'. Baldness is less likely but still possible, and something I'm still crossing my fingers to not have happen. I also was thinking, 'dangit, if my ass gets super uber hairy I'm going to have to wax it...' Not looking forward to waxing, but see it as the lesser of the two evils, as I'm not fond of the concept of looking like I'm wearing pants even when I'm naked.
Oh. And cancer. Knowing I won't be able to afford having my innards gutted surgically any time soon, I was/am worried about developing baddies up in my reproductive system. But I figure hey... I'd rather have lived and gotten cancer then never pushed through, secondly if I did begin to develop obvious precancerous cells, I'd probably have an excuse to have things removed under medical coverage, so, thumbs up either way.
It wasn't a question of 'will I go through with this or not', more like 'I HAVE TO DO THIS, am doing it no matter what, so how much will the repercussions suck?'