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 I also realized, after the episodes wore off, how completely wrong deconditioning theories are about ME. Once I was safely able to stand again without symptoms, the first time I went up stairs after a month was way easier than it had been for a very very long time. And as I went up the stairs again and again, usually twice each day, it got harder and harder. Now that I don't need to lay down at all during the day, I usually only go upstairs once, and that helps a bit with my overall ability to be active in more useful areas ... Ideally I'd like to have no stairs to go up, since it seems to improve my physical condition when I avoid them completely.