"Tuberculosis and lymphoma are diseases in which night sweats are a dominant symptom...other diagnoses to consider include human immunodeficiency virus, gastroesophageal reflux disease, obstructive sleep apnea, hyperthyroidism, hypoglycemia, and several less common diseases."
Diagnosing Night Sweats, American Family Physician, March 1, 2003
http://www.aafp.org/afp/20030301/1019.html
What tests have his doctors ordered for him?
People infected with Babesia may have this symptom.
I hope you can get to the root of the problem.
Wishing you the best,
Carol
Has his physician checked him for swollen lymph nodes ?