Hi.
It sounds like you have a glitched sim or a glitched bed/couch.
You can test this by just copying the old bed/couch and replacing the original. If everything works fine from now on, the bed/couch was glitched and your problem will now be fixed.
If they persist it could be that the sim is glitched and that is harder to solve. First type in resetsim + name of sim in the cheat window, if this doesn't clear it up try moving the sim from the household in edit town and re-add it to the household again. Alternatively to move the whole family to the clipboard and then move them back in the house.
If you have been playing this particular save file for a very long time it could be that the file has become so buggy that the problem can't be fixed. If you look at the game moderation page you'll find some tips on mods that will help clear up error in your game and make it run smoother. But please try the other suggestions first.