I also noticed while I put my latest book together and spent days in my office chair - the old problem was coming back. I had suspected it before, now I was fairly certain. Something about sitting in that chair was putting pressure on some vein and causing the problem.
Last night, I took a gamble. I ordered an old (gasp), used, little bitty (to me) netbook. I figured I could keep it by my bed and write (or whatever) in my bed with my legs stretched out straight. I don't know if it will make me crazy, being so small, but it only weighs about 3# and supposedly the battery (or the new one I buy for it) is supposed to last for 9 hours. I am really not into the thought of lugging this Dell around, even if it is only a matter of a few feet.
The best part of it - is that it has WinXP or Win7 on it! Is supposed to come with Win 7, but there again - being used ... I can write to my heart's content and transfer my files to the Dell. (In a perfect world) There I go - planning again.