nitrogen narcosis, but because the feeling leading up to doom can be seductive, even hallucinogenic, divers sometimes call it "rapture of the deep."
Because the world thrives on balance, a similar condition exists up top. This one is created by elevated levels in the emotional bloodstream, a jacked-up sense of longing and desire for someone. There is never any reason for it; when someone is a desideratum all logic is lost and the only thing that makes sense is a deeper dive.
Where you're down there up here it can be frightening, even terrifying. The instinct is to swim away, head for the surface, look to the light. People who do this say they're moving forward and getting on with their lives, and once they get away from the desideratum they find excuses for their seemingly mad behavior; they chalk it up to infatuation and temporary insanity and only occasionally look back over their shoulders at the seductive memory. Perhaps they even convince themselves that they're better off.
But are they? They're safer, to be sure, but safe is usually boring, a place for dull edges and minds. Exhilaration is often scary — respirations quicken, pulses race — but that's where life is meant to be lived, in a land of piercing possibilities, not colorless certainties. There is no magic in ordinary days. There are no bells.
Then again, those who choose to dive deep while listening to bells face one real danger: their diving partner can get scared of the euphoria and make a beeline for the supposed safety of the shore, leaving them to fall ever deeper into the rapture. The beautiful chimes become a death knell in the dark, its resonance so loud you are deaf to all other sounds. But at least it is beautiful.