Hi,
Night sweats are the occurrence of 
excessive sweating during sleep. It can occur due to infection, hormonal imbalance, cancer, psychological conditions, drug-induced and several other causes. Considering his age, psychological morbidity and treatment following are possible causes which need to rule out in his case: 
-Hot sleeping environment: Hope it is not in his case. 
-Residual anxiety and 
depression. 
-Hyperthyroidism: It is also associated with anxiety. For evaluation get his serum T3/T4/TSH done on empty stomach. 
-Autonomic over-activity: common in anxiety and hyperthyroidism. 
-Substance use like alcohol and heroine Although night sweats can occur with 
sertraline but in clinical population it is rare. It is better to rule out above condition first as a cause for night sweats. 
The following situation will favor night sweats due to sertraline: 
-If it is started after initiating treatment with sertraline. 
-If it is stopped within 2 weeks of reducing doses or terminating treatment with sertraline. 
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. Ivan R. Rommstein, 
General Surgeon