It sounds like you are having adrenal problems. When you take prednisone for more than 3 or 4 weeks, your adrenal glands stop make cortisol. Cortisol controls how much energy have. To your body, prednisone looks like cortisol, so when you take prednisone your body thinks you have plenty of cortisol, so it doesn't make any more. As you taper prednisone down to around 5 mg of prednisone a day, your adrenal glands need to wake up and start making some cortisol again. But it can take quite a bit of time for the adrenal glands to get fully active again. Depending on how long you've been taking prednisone and the dose level, it can take several months.

Tapering from 40 mg of prednisone a day down to 0.5 in 5 months is very fast. Most people take at least a year, and some people take a lot longer. PMR usually lasts a year or 2, and you need either prednisone or some other drug to control the PMR while it is active.

I would recommend you talk to your doctor about increasing your prednisone dose and then tapering slower to allow your adrenal glands time to wake up. You might need to go back to somewhere between 3 and 5 mg a day, and then taper slowly to see how your body handles ease dose. From 5 mg down to 0, I tapered 1 mg every 4 weeks.