If you have a laptop/palmtop/iPad/Blackberry/something wireless you can write with, the simple solution would be to go out to those places and write there. If you only use a desktop computer though, it might be a little more complex.
Maybe go to these places, (or even your backyard or wherever,) and take a pad and a pen and just scribble down character ideas, plotlines, snatches of text, and whatever else comes to mind, then go home and organise it on the 'puter. Open up windows nice and wide and make sure there's plenty of light in the room, then just sit down and do it!
I hope this helps even a little bit, I know how you feel and it is horrible to just be getting up and wandering around the house every five minutes because you don't feel like sitting down any longer. :[ Good luck!