Sean Kingston's Savior -- He Was Puking Blood

Jonathan Rivera, a member of the Coast Guard, says he was driving his boat around Star Island on his day off ... when he was called over to the accident scene by a man and a woman on a jet ski. Rivera says he noticed an empty jet ski, a woman in the water floating (she was wearing a vest and complaining her head hurt) and Kingston.

Rivera says the two people on the jet ski were trying to hold Kingston up, but they were struggling to keep his head above water. Rivera says Kingston's size was a problem for them, as his life vest had come off.

So Rivera says he jumped in the water and noticed Kingston was "puking up blood out of his mouth."

Rivera says he wrapped his arms around Kingston and held on to the jet ski to help keep Kingston's head above water. Rivera said Kingston was "convulsing and throwing up blood all over me" -- but said he didn't notice any head trauma.

Rivera tells us he held onto Kingston for about 15 minutes, until a police boat finally arrived. Rivera says he doesn't think he could have held on much longer than he did.

Rivera says when help arrived, he told Sean he was going to be okay. He says Kingston repeated back to him, "I'm going to be okay."

When it came time to get Kingston into the boat, Rivera says Kingston was able to follow directions, though he did need some assistance getting in.

From there, paramedics quickly came and cleaned Kingston up and rushed him to an ambulance that was waiting nearby.

Rivera, who says he didn't recognize Kingston until well into the rescue, tells us, “I mean regardless of whether I was in the Coast Guard, I would have still jumped off to help him. He needed help."

Jimmy Vega, who was with Rivera at the time and assisted in rescuing Kingston, talked to a local reporter (see below) and explained, "We were about to turn back around [and go home] when we noticed him. I truly believe if we did turn around, he would not be with us today."