Whether it is prednisone withdrawal symptoms or PMR coming back really is hard to determine when we taper below approximately 7 mg.

I had a very difficult time at that dose too. Prednisone withdrawal symptoms are caused by adrenal insufficiency. People who attempt to decrease their prednisone dose after a long time may experience symptoms such as:
muscle pain
joint pain
fatigue
nausea
vomiting
low blood pressure

As it turns out, the adrenal glands make most of the body’s cortisol however, the body cannot immediately produce enough cortisol again to make up for the lower doses of prednisone. This results in withdrawal symptoms. or adrenal insufficiency.

The body uses cortisol for many functions:
mediating the stress response
regulating metabolism
managing inflammation
mediating the immune response
managing the levels of blood sugar reaching the brain
reducing insulin and increasing glucagon levels in the pancreas

Prednisone manages inflammation until we attempt to wean ourselves off. Taking prednisone for a long time shuts down the body's natural ability to regulate inflammation. This includes the inflammation caused by PMR. I believe the difficulty in tapering our prednisone dose below 7 mg is a combination of adrenal insufficiency and PMR.

It is necessary to wait until our adrenals begin to produce adequate amounts of cortisol again. This process can take months to happen. In most cases , it eventually happens but it doesn't always happen.