I'm with you... or rather I was. I went from 10 hours of activity a day (athlete all my life, then military, then dancer, then extreme sports person) to being STUCK doing NOTHING while preggers with my son (saved his life however).
The UPSIDE is that it's unlikely you will be as unlucky as I was. I had a weird metabolism thing happen when I was pregnant (also had cancer stuff going on... my body reeeally flipped out), that caused me to double my weight while pregnant. So it took me a LONG time to get back in shape (we're talking a couple years). Most women I know stuck on bedrest are back to "normal" within 6 months. It took me much longer, since I was over 300 lbs when my son was born.
The hardest thing was the expectations I'd place on myself. Years worth of experience told me I SHOULD be able to do x, y, z. I had to toss those, and relearn what my body was then capable of.
Totally doable, however. Just took some time.
Strong 2nd to getting active mentally (reading, writing, movies, music) to keep from going completely bonkers. Small physical movements will helps also. Ever wanted to learn to play an instrument (violin, guitar, fluite, winds, anything)? Any chance you're an artist? Or knit/sew? Or practice tattooing? Anything that can keep your arms moving will help lessen the insanity. Ditto massage I found helped a great deal. Maybe *I* couldn't move my muscles, but someone else moving them helped a lot.