Sorry to hear you are having this same problem, katielo!
Lucky me, I had another, earlier save file... I think I talked about this in some another thread, but when this happened yet again on my file (and this last time was without any travelling), I tried different things to see if it could be fixed somehow. I managed to split the household and get rid of the sim that was stuck. She was sleeping, and strangely enough the Zzz's kept floating where she had been even after I moved her out, but the rest of the household seemed to be fine. I kept playing and first, the other, still "normal", sims seemed to be OK, but over time they started acting strange, one after another. Popping invisible and back, teleporting around the house, canceling their actions etc etc. Some furniture became unmovable/unusable. It seems like there's no cure if this thing starts, it's like it spreads if you keep playing with the same file...
There's many different topics around the forum about similar problems and it seems to me there is no fix to this. Still, someone said that the family could be restored if you save it to the bin and copy it to a new town/file, but I have not tried that myself. Maybe you could try that, katielo? (I deleted the bugged file earlier, so I can't try to see if it works. Somehow, I doubt it, as the game seemed so totally messed up after this bug, but I'm hoping someone will prove me wrong.)
These days, I make a new file with "Save As" every time I play more than an hour just to make sure. It happened to me once without travelling, so I just want to be 100% sure.