No, I don't think it is stress. 20 mg is a turning point on pred.
It is exactly the point where you might start having problems because at that point your body has to kick in and start doing something that pred was doing, before. You might have to slow down on the pred taper, by 2.5 mg weekly.
OR you could try using Entocort to help you taper off pred...my daughter tapered successfully of pred by introducing Entocort when she was at 20 mg. Taper schedule"
week 1: 1 pill Entocort, 20 mg pred
week 2: 2 pills Entocort, 15 mg pred
week 3: 2 pills Entocort, 10 mg pred
week 4: 2 pills Entocort, 5 mg pred
week 5: 3 pills Entocort (full dose), 0 mg pred