Some people here are so ignorant. Maybe first look up things like tourettes syndrome and trichotillomania and then talk. These are anxiety compulsions that can only be slightly controlled.
As for Shabbos, nail biting and hair pulling is midirabanan.
Second, compulsions are anus. The gemara in Eiruvin discusses similar situations.
Third, dirabanans are mutar in cases of tzar. The anxiety of compulsions is a great tzar.
This does not mean that we should do these things lichatchila. But if one ends up doing it because of an anxiety compulsion, it is not a an issur.
On the other side, these kind of issur look alikes might stem from or be suggestive of deeper issues, so it is always something to you need to be mifashfesh.
These things are also always meant to humble a person.