random injury - how long to wait?

I was doing the 30 ds pretty consistantly until monday...Then tuesday i couldn't do it (i didn't want to get sweaty because i didn't have time to unsweaty), so i went for a super brisk walk and i was fine. I hopped on a ferry that afternoon, and an hour into the trip (sitting, doing nothing) my knee went kablooie. Total pain, no good reason. I limped and swelled for two days... yesterday it was much better but far from perfect, today it's 80% maybe a little more, but i can still feel it.

What is the line between taking care of myself and making excuses? I'm on level 2 and there is a fair amount of planks, and jumping... I'm not super obese, nor am i super out of shape, so there is no reason for me to NOT be able to do this kind of thing! i thinkit was a freak moment, and I'll be fine (i didn't get it looked at, as it was feeling better every day)

When should i put myself back in the game? I can't live off the food i get without exercise calories to eat back (don't judge me on my lunch today, that was a rare occasion)

tia!