I know this is sort of a necro from an old post, but I'm going to let you know that this happens if you use the cheat to remove the buff from your Sim. Although your Sim will appear in his/her normal state, the Sim will still have some of the issues with skeletons. (Food goes through the Sim, no romantic interactions, no outfit changing, etc.)
If you have done the cheat and are now stuck in this mode, your best bet is to use the Balampalsoh Death Relic. If you use a common gem in it, the buff only lasts something like 10 or 12 hours. After the buff expires on its own, the problem will be solved for the Sim. You can buydebug the relic pieces, or - if you're like me - you should have a dozen of each part in your inventory from doing excavations hundreds of times, and you can just craft the relic for yourself.
So, note in future: Don't cancel that buff on your Sim just because you don't want to see the Sim as a skeleton. You just have to deal with it. 🙂
The developers think the buff is a BLESSING. I don't know why, since when it expires my Sim always has drained energy. (And since she has the Never Weary reward trait, normally her energy bar never goes down.) I view this so-called "blessing" as a curse. I really don't like the skeleton idles.
