Fatigue occurs in people who don’t have MS, so be aware that your fatigue may be attributable to factors other than MS -- for example, aging, menopause, anemia and depression. However, MS lassitude is distinguishable. Fatigue is a most frequent cause of MSers leaving the workforce. The National MS Society lists options to deal with and help manage fatigue.
Extreme temperatures may heighten problems causing rapid loss of control and balance. Luckily, these symptoms are generally not permanent and the problem relaxes after temperature correction. A cold cloth on my face and forehead allows my energy to return. Blurry vision, known as Uhthoff's sign, usually clears up with cooler temperatures. But temperature sensitivity is more than just heat. Extreme cold may cause an increase in spasticity.
You know you are having a spasm when your muscles tighten and make movement, especially of the arms or legs, difficult or uncontrollable. Here is a site dedicated to understanding spasticity regardless of the cause. It includes a gallery of 12 people, chosen for a calendar, who tell their stories. Three of these are MSers, Deanne, David, and Barbara.