Appeal. Get some help to do so - have you tried the CAB or Fightback? Keep appealing love. Yes I know the system, my husband has ended in tribunal 2ce - 1ce for ESA and once for PIP... Always base things on a worst case scenario love - NEVER underplay anything.
It's expected to have a dip when you finish therapy and then to have this appeal decision must feel like a real kick in the teeth... You can get through it though. Keep fighting those thoughts - that's all they are....