Focal hyperhidrosis isn't medically serious. Other forms of excessive sweating, though, can signal underlying medical problems.
Sweating all over the body at once is called generalized hyperhidrosis. It's frequently caused by diseases affecting the whole body. Infections, hormone problems, cancer, or nerve problems can be responsible. It often occurs during sleep, unlike focal hyperhidrosis, which occurs only when awake.
Anyone with all-over body sweating should see a doctor as soon as possible.