I wondered the same thing about "flares" ... until I went thru a couple in a row and now that my body has "calmed down" I know the difference.
They are very intense. For me one was a bad case of Optic Neuritis (which made my diagnosis but was terrible for driving, I knocked the mirror my car!).... but it subsided so that my vision has stabilized now after about 2months of all the little nuisances off and on. It involved unequal pupils, some headaches, diminished color detection, and peripheal motion sensed that wasn't there. Permanently now it's the diminished color so far but all else has "calmed down". My car is safe again.
The second major flare came on the heels of my LP, and it was all spasticity, which I never knew what that was til I lived it. Severe cramping in both legs, major charlie horse cramps in the calves and particularly the right leg for days on end without relief, made my calves look like marbles under the skin. Muscle relaxants & Pain meds provided temporary relief but by the next day it'd be in full force again.
Then one day about 2 wks ago (it probably was the cool Alaska Vacation!) it all subsided. Now it's the normal mild pain, mild cramps, mild aches etc.
Some flares can be bad enough to put you in the hospital too, so far I've been very lucky not to have that happen. (knock on wood, I'm fighting Acute Bronchitis right now and it's not subsiding very well).
Hope that helps... everyone is different so you have to sort it out for yourself but after awhile you'll know when it's a full blown flare and when it's just a situation.
Fear knocked ~ Faith Answered ~ No one was there! :)
~ Ephesians 6:13 ~ * ~ Psalm 27:1 ~