It may not be the prednisone that's the cause of your up and down days, it could be the course of the PMR itself. I'm 78 and was pretty active myself until last fall: got a bad cold that became pneumonia, then problems with my feet, then a horrible GI thing, then the pain and weakness starting in my lower legs, knees, and thighs. I hate prednisone. It tastes bitter, it wrecks my stomach, makes me moody, and I gain weight. But at least I can get up out of a chair without help and walk without a cane or walker. When I try to taper lower than 10 mg. (prednisolone not prednisone because it's easier on the stomach), the pain and weakness come back. My rheumatologist said 6-12 months before it resolves, though it could go on a lot longer.