You have my sympathies mate, "Gute Besserung" ("get well soon").
A lot depends on you, and it takes discipline to keep to the regime laid down by the quacks - but you WILL regret it if you don't - DAMHIKT!
Many have said reading which personally I always find a great relief - there's so many "areas" that you can "escape" to, and personally I rate my Kindle very highly indeed - but NOT for any sort of "technical" books where you need to study drawings, photos, etc - Kindle handles those badly, but is great for print only - how else could you carry, say, 500+ books in a thing smaller than the average paperback?
Someone suggested learning Sketchup properly, which is obviously a great idea for someone who is a member here, and to that I'd add learning Photoshop (the "Lite" version is more than powerful enough for ordinary mortals) and again, that, together with learning how to post pics here, obviously has its uses for a member of UKW.
Re walking, it's good medically, but as said, can be boring. Have you got a friend or neighbour with a well-trained docile dog (not one who'll drag you off your feet)? If so going walkies with him/her is also a good way to add interest to walks.
And if your thoughts run in that direction, how about a go at learning a language, a musical instrument, or some practical geometry/maths (again, useful in the shop later). Lots of such tutorials on line as I'm sure you know.
HTH