really weird ...

so this just happened, and I wondered if anyone else could relate (or give me some sort of explanation)

I've been doing fairly intense workouts for the past (almost) two months. I was in pretty good shape to begin with, so I really haven't experienced any muscle soreness or weakness. I work out Monday-Friday (sometimes on Saturday) Well, this Monday, I had to take the day off to go to an audition. Tuesday morning, when I woke up, I could barely move my legs. All of a sudden, I'm having intense muscle pain and feel so sore I can't even walk up and down stairs. this is really weird.

any thoughts?? I am completely baffled.