Kevin Hart is on the mend this morning after going under the knife Sunday less than 24 hours after he injured his back in that horrific car accident.A source connected to Kevin tells us doctors completed successful back surgery on Kevin Sunday evening. Another source told us the comedian is expected to remain in the hospital for at least a couple of days while he recovers.TMZ broke the story ... Kevin was miraculously able to walk away from the accident early Sunday morning on L.A.'s treacherous Mulholland Highway -- with assistance from a bodyguard -- but was rushed to a hospital with what cops called a "major back injury."TMZ got video of Kevin's wife, Eniko Hart, on her way into the hospital. She says Kevin's "going to be just fine." It's clear the previous day and night have taken a toll on the Harts -- looks like Eniko had just made a coffee run -- but she says Kev's awake and recovering.NBA star Chris Paul visited Kevin at the hospital Monday. They're close friends.Jared Black, the man who was driving Kevin's vintage Plymouth Barracuda at the time of the accident, was pinned in the crushed vehicle and also seriously injured. He was airlifted to UCLA Medical Center and we're told he's surrounded by family members as he also recovers.Click here to watch video of Kevin’s wife going to the hospital