I would be concerned too. I have been on lithium and abilify, and personally I didn't feel that the abilify did much. When they tried to d/c my lithium, things got unstable pretty quickly. Just keep an eye out and let them know the moment things start to feel funny. I had that hunch too, and I was right.

Edit: I've never been stable on less than 3 meds (2 mood stabilizers and 1 for anxiety)