Its natural to worry about EVERYTHING! blob but you be amazed how quickly you are up and about after surgery and how well you feel, tired definitely and a little blotted maybe but the recovery for me was really quick.
I had a bypass as well, into theatre at 12.00 noon and walking around the corridors on the ward at 9.00pm the same night. They want you up and about quickly.
Over the next few weeks I was out for a walk everyday and pottering around the house, doing nothing heavy though that's important, I got tired but just through in an afternoon nap for a few weeks and it went great. I live alone as well so I was looking after myself.
So really its not long before you are up and about, just nothing to strenuous till you have get your doctors OK, mine was at my 6 week follow up and it was only then I started the gym.
Hope that helps.