I think this is standard practice. I know that SSDI is reevaluated every so often as well. The burden of proof is on them - they have to prove that you are no longer disabled, which isn't as easy as it may sound. I know how nerve-wracking it feels, waiting. Familiarize yourself with the appeals process, just so you know what the next step is, should they decide to deny you. That's great that your psychologist is going to write that letter for you. Find something to distract yourself from it for a while. Hang in there.