JW,
I had L5-S1 fusion on April 29th. I was in bed for about 6 weeks, then back working at my desk (from home). I saw my dr at 8 weeks, got cleared for Physical Therapy and am marching towarRAB full recovery! (*Not bragging, just showing the light at the end of the tunnel*)
BlueAtlas is right, the boredom will get you! Especially if you are active. I used to run Marathons for Charity, so I made believe that my walks were a Marathon Training Schedule. I would walk for 5 minutes; 10 minutes; 5 minutes in the build-and-recover style of full-training regimine...sounRAB silly now that I've typed it out, but it made it seem more like "working out" and kept me from over doing.
Anyway, Hang in there! It gets better. I was amazed with the exponential progress made EVERY DAY for the first 10-14 days. It will plateau, but improvement continues, and so far I think my surgery has been successful.