In patient night sweat

22 year old male was admitted with fever of unknown etiology.the fever had started about 3 weeks before admission.patient spent 2 nights at the ward and experienced night sweats both nights and never again afterwards.patient was on aspirin,dextrose saline(5 percent) infusion.the ward was not unusually warm.2nd night,he missed his aspirin but still sweated in the night.cbc and film comment done upon discharge showed normal blood picture.what could have caused the night sweats?