John Clark Gable DUI Arrest -- I Wasn't Drunk, But I Did Black Out Before Multi-Car Wreck

The son of Hollywood legend Clark Gable claims he was not drinking alcohol before the multi-car wreck that led to his DUI arrest -- but does admit he went unconscious ... and says he has a history of brain aneurysms.

TMZ broke the story ... John Clark Gable was busted Tuesday in Malibu after allegedly smashing into 6 parked cars on Pacific Coast Highway.

Gable tells us he lost consciousness ... and says the last thing he remembers is getting cut off by a van, and when he woke up he had hit a phone pole.

Gable claims he "absolutely was not drinking" ... and says the only medication he's currently taking is for a minor leg injury from mountain biking.

However, Gable says he had 2 small brain aneurysms --weak bulging spots on the wall of an artery -- back in 2006 and another in 2009.

Brain aneurysms can be fatal, but Gable says he had corrective surgery both times.

Gable says he's going to a doctor to get his head checked out ASAP -- but stresses he doesn't know yet if an aneurysm was behind yesterday's accident.