Wish I could give you some wisdom on this, but I've never really experienced clear-cut differences enough to know when I'm in a flare and when I'm not. Something is always acting up, then it's something else, no 2 days are the same. Of course, some days are harder than others, but it's not day and night.
Sorry that's not much help! I guess I'd say just listen to your body and if it needs extra rest, extra meds (within reason) or whatever else, go with it.
I have thyroid issues too, and never know what's causing what (sigh!) I always get this picture in my mind of the old Star Trek show, where Dr. McCoy would run a scanner over someone's body and in a few seconds, that would tell him exactly what the problem was. If only! I hope your pain fades away.
fibromyalgia, herniated disc L4-5, (with sciatica), bulging disc L5-S1, other assorted spinal deterioration, scoliosis, Hashimoto's, IBS, migraines, tachycardia, hearing loss (probably from Menieres Disease)