My rat acts funny

Question
I have three rats two males and one female.  Well one of my males acts very strange.  His head swings from side to side rather violently and he falls over or off of things because of it.  He freaks out when we touch him.  He also has a biting problem he doesn't break the skin its more like a nibble but every time our hands go in he tries to nibble on our fingers.

Answer
 Head bobbing and loss of balance can be due to something simple like an ear infection which can be treated with antibiotics or something more severe like a brain tumor, stroke, or other neurological problem.  The biting is probably due to his condition; he is scared and may be in pain, or he may simply not be capable of realizing your hands are not food.  Either way, he's going to have to see a vet.  If it is an ear infection it can be cured but if it is anything else the chances are not good.  I hope everything turns out okay, good luck!