This was me at 300 lbs, those days are behind me for good!!
"If you worried about falling off the bike, you'd never get on."
"Pain is temporary. It may last a minute, or an hour, or a day, or a year, but eventually it will subside and something else will take its place. If I quit, however, it lasts forever."
LOL, hey at least you're on line for that scary roller coaster, I'm still watching from behind the fence! I don't know why, I've always been active, but I'm finding it harder and harder. I used to be able to push so much more. Now I'm just trying to build back up (endurance and confidence) then I'll have to give the P90X program a try. If you search you can find other people's experience on the program, but then again you may want to get into it on your own and see how it goes before comparing notes. Just remember starting anything new is always the hardest, its pushing through the initial soreness etc that gets you where you want to go.