Some men just sweat at night....high metabolic rate and all that. But if it is something that has started recently it can be a sign of an unnoticed infection, such as sinusitis, or a deep tooth abcess, which dont always cause a lot of pain.
Another cause can be allergies, particularly if you are reacting to house dust mite.....
Essentially there are a lot of things it can be. If its a problem a trip to your gp might be in order.