Not an injury forced lay off, but many moons ago (nearly 30 years), I got chicken pox. Bored outta my tree, only 4 channels on tv, no interweb, and living on my own (no chance of visitors with me covered in itchy spots), I got my old guitar out and relearned. It certainly passed some time on.
Or, you could have a go at learning a language.
Best wishes, heal well.