Take ours for instance. Yesterday, the one with no fur on the top of his head had a birthday, so last night, we allowed them to go out. Today, they are both moaning and groaning, and seem to be totally incapable of doing anything! they are creeping round to avoid loud noises, and are even bigger wastes of space than usual.
If it was not for the fact that I am such a caring and thoughtful pet owner, I'd just throw them out on the street right here and now, but as it is, I'll give them a couple of hours to see if they improve first.