Diddy Hospital

Diddy was transported out of federal prison early Saturday morning for a medical emergency ... TMZ has learned.

Sources at FCI Fort Dix in New Jersey tell us ... Diddy left the prison grounds early Saturday morning to get treatment for a head injury. Presumably, he was taken to a nearby hospital, but we haven't confirmed that.

We're told the ambulance pulled out of Fort Dix around 1 AM ... but, apparently, the injury was not life-threatening, because our sources say he was conscious and speaking when he was taken back to the prison before sunrise Saturday.

It's still unclear how Diddy hurt his head.