I agree with the others that doing something is better than nothing. I cracked the Head of my left Humerus about 3 1/2 weeks ago in a paceline. I've been in a sling until yesterday. I borrowed a staionary trainer, but it didn't work out. I've been doing hiking(non -technical terrain, of course), of about the same time as my biking. It's frustating, but think of things to do after your rehab. Since you fell, I would urge to go do some Helmet, glove, and whatever other clothing that got it during your fall shopping. It will give you hope that you'll back out on the bike. Also, it's helping me to focus on my bike related plans after my rehab