It was far from the first time Dean had belly-flopped into a pool, but it had been a while since he'd done so, and the shock was never fun or particularly something you got used to. He had managed to suck in a little water as he went down which was a horrible combination with the air being knocked out of him. Still, he was experienced enough that it took him only a few seconds to recover his wits and try and make for the surface, rather less coordinated than usual.
He also hadn't noticed that the person he'd faintly seen in the doorway had launched herself in his direction in a rescue attempt.