My 17 month old daughter never napped good when she was oversuppressed.  She has salt wasting CAH.  I questioned her ped. endo about this, but she said there is no scientific evidence that suggests that oversuppression leads to sleeplessness.  However, I posted about this on the board before and got a lot of responses from parents.  A lot of parents agree that their kids don't sleep well when oversuppressed.  Fortunately, we have cut back on the Cortef enough to finally get a 17OHP level and now she takes a 2-2.5 hour nap everyday.  Good luck!