El Chapo can't remember a damn thing and is depressed as hell ... and that's why his lawyers are begging a judge to let a doc take a look at him in jail.
Lawyers for the drug lord want the judge to allow for a neuropsychological evaluation at the Metropolitan Correctional Facility because in just the last month he can't remember people, places and events.
In new legal docs obtained by TMZ ... lawyers say Chapo suffers from headaches, ringing in his ears and throat pain ... claiming none of it has been looked at by doctors. Plus ... Chapo's been denied from buying simple things like bottled water, batteries for his radio and personal hygiene items.
Chapo's condition, lawyers claim, is a result of complete isolation, frigid cell temps, lack of clean bed covers and no fresh air, among other things. Lawyers also claim shortly after just one visit from his sister, the government revoked her visa and she can no longer enter the U.S.