Dy mouth can be caused by many medications, or even physical conditions. Sjogren's syndrome is one such condition. If you don't take any medications which could be causing this (decongestants are big causes of dry mouth, as are anti-Parkinsons's medications -- I take Mirapex so that is the cause of it for me), you should mention it to your doctor at your next appointment.
It could just be minor-it's cold outside! You just have a dry patch or something- or something serious, like what the others were hinting about.... Ou could possibly be a diabetic... Someone I know is, and that's what happened to her, how she found out.... Your should talk to a doctor about it though... (: