Weight Loss Journal - Currently doing P90x

So I officially started P90x tonight. It is everything I read about. Tough and very challenging. With my size, I came no where close to keeping up with them. I did as many push ups as possible and switched to doing them on my knees. Did these until I couldn't do any more. I poured sweat the entire time and felt in the end I pushed myself as hard as physically possible. I have the same natural high anyone gets when starting something new and I hope it continues.

For that are doing P90x and reading this. What do you do when it's physically not possible to get a workout in. I know it's early but I'm already worried that I will miss day 6. Not sure I can double up on a workout at this point so I will probably just continue on the following day.