Police are investigating the death of a 64-year-old man whose lifeless body was found inside his Upper East Side apartment Wednesday morning.

The unidentified man was discovered by police during a 7:20 a.m. wellness check at his apartment on East 83rd Street near Lexington Avenue, cops said.

He was found unconscious in the living room, lying face down with a head wound, police said.

It’s unclear who called cops and told them to check up on the man.

EMS workers responded and pronounced him dead on scene.

The city’s Medical Examiner will determine his cause of death.