You don't... Well... Basically, you get into a fight you can't win, and you fall for a long time, and then you fatally hit the water. While the shock and suffocation slowly kill you, you experience a hallucination in which you explore mysterious depths. You're joined by flittering, colorful, seemingly friendly fish, which indicates a subconscious need to... well, not die alone. You don't explode into light, you ascend into it. A lot of people who very nearly die report experiencing travelling towards the light, and feeling at peace. It's very likely a neurological event associated with approaching brain-death.