Chronic illness sucks. It’s hard to keep moving when you have no energy. If a walk to town will wipe you out for days then you most likely won’t and, honestly, probably shouldn’t. Equally, you don’t want to not move at all as you can seize up. Lots of exercise advice is aimed at people who are healthy and able, or at least able. Gradually building up activity doesn’t work if your energy levels won’t increase with it; you can be left feeling worse than you did and less able to move.