Hyperthyroidism means that your body has too much thyroid hormone, which controls how your body uses energy. Too much thyroid hormone can make you lose weight quickly, have a fast heartbeat, sweat a lot, or feel nervous and moody. If it isn't treated, it can cause serious problems.
E. Gregory Thompson, MD - Internal Medicine & David C.W. Lau, MD, PhD, FRCPC - Endocrinology