Sure, but I don't think it's ever advisable to be sedentary in any illness. I always felt I benefited from keeping active even though it was hard at times. I suppose every case is different. Even though I suffered profound exhaustion, I never lay flat for a whole day for example. I try to keep reassessing my physical limits.
I had a sudden bout of intense OI issues hit me twice in the past two years that I've been sick. Each time, sitting up even for a few seconds was extremely difficult and I was unable to think while doing it. I had no choice but to "lay flat" for 3 weeks during the first episode, and 1 week during the second episode.
It was an extremely unpleasant experience - laying down all day is painful and interferes with being able to use my laptop much at all. I did stretch my muscles during this, and would of course get up for very quick trips to the bathroom or to grab prepared food from the kitchen to eat while laying down. I also started "exercising" my legs a bit while still laying down when they started feeling restless.
One useful thing did result of my weeks of laying down - I realized how strongly my cognitive problems are connected to orthostatic intolerance. I was able to think clearly all day while laying down, which was a refreshing change