What Snoopy said.
I do not go into a full-blown exacerbation from over-doing things, or from heat. I can go into a exacerbation from infections (and an increase in body temp due to infection), but not from external heat sources.
Are you sure you do not have an infection of some sort; tooth? bladder? sinuses?
If you are absolutely sure you don't . . .
Over-heating can cause a psuedo exacerbation for me, which means my body reacts with MS-symptoms . . . but those symptoms let up when I rest and remove the trigger (like heat, stress, over-doing things, etc.). If you rest up and DO NOTHING for a few days, theoretically the symptoms should let up.
If, after a few days of rest, you are still not doing well . . . it may very well be a exacerbation, defined as "new, or worsening of existing symptoms, lasting longer then 24 -48 hrs". As Snoopy said, steroids are an option . . . but I don't take them unless absolutely necessary as there are risks and side-effects.