What Is Considered A Relapse?

Since Saturday morning I have had severe lightheadedness along with muscle pains, a headache that's not going away and itchiness. I've not got a cough, a sore throat or runny nose. Just these symptoms that are persistent and not easing at all. I've asked for a callback tomorrow when the MS nurses are running a telephone clinic but I don't know whether I'm doing the right thing . Can anyone advise please?