Night sweats are episodes of nighttime sweating that soak your nightclothes or bedding and are related to some underlying cause. You may occasionally awaken after perspiring excessively, particularly if you are sleeping under too many blankets or if your bedroom is too warm. These episodes are usually not labeled as night sweats and, although uncomfortable, typically aren't a sign of a medical problem.

Causes
Medications that can cause night sweats
Night sweats are a common side effect of many medications, such as:
-- Depression medications (antidepressants)
-- Drugs used to regulate your hormones (hormone therapy)
-- Drugs that lower the level of sugar in your blood (hypoglycemic agents)

Medical conditions that can cause night sweats
Diseases and conditions that can cause night sweats include:
Infectious Mononucleosis
Anxiety
Autonomic neuropathy
Brucellosis 
Carcinoid syndrome
Endocarditis 
HIV/AIDS
Hodgkin's lymphoma (Hodgkin's disease)
Hyperthyroidism 
Leukemia
Menopause
Myelofibrosis (a bone marrow disorder)
Non-Hodgkin's lymphoma