If you are a woman, you could be suffering from change of life symptoms. The best advice is to see your doctor. Maybe your thyroid is off. He can run tests and put your mind at ease.
Anxiety, nervousness or stress might be the causes. Having to speak in front of a large audience, or being suddenly embarrased may result in profuse sweating.
Being out of shape can cause lots of sweating with little exertion. Being overweight and having certain medical conditions can, too. See your doctor to be safe.