was either wasted, exhausted, or both following his DUI arrest Friday morning ... because he passed the hell out once he got inside the squad car -- and TMZ has obtained dash cam footage of the entire bust.
TMZ broke the story ... the rapper was popped
in South Carolina around 3AM Friday after police determined he had been driving under the influence.
It wasn't immediately clear whether X was busted for alcohol or some other substance -- but based on the dash cam footage, it appears to have been for alcohol ... and not just because X was a little sleepy.
In the footage, the cop asks X if he's been boozing, and X says he had one drink -- but later it sounds like he admits to drinking "4 or 5" (the audio is pretty bad). Despite the drinks, X insists he's not too drunk to drive. The cop doesn't buy it.
X was booked for DUI and hauled to a nearby station. He was released from custody roughly an hour later.