Police say the crash happened near Highway 99 and Herndon Ave. in northwest Fresno.
They say an 18-year veteran of the department appeared to be suffering from what appeared to be a medical emergency inside his patrol car.
He was removed from the vehicle and given aid on site.
The officer was then taken to Community Regional Medical Center, where he recieved Narcan.
Police say he is now alert and talking.
They say he was on a prior call regarding narcotic activity but that they are investigating the cause of the crash.