Critical Down

A Critical Down (クリティカル・ダウン) is a phenomenon that occurs occasionally during a Dive, in which the Reyvateil rejects the Diver and expels him or her from her Cosmosphere.

However, this also has more serious consequences, as in cases of extreme incompatibility, the H-Waves of the people involved will be completely unable to synchronize with each other and the end result will be that the H-Waves of the Diver will be absorbed (devoured) by the H-Waves of the Reyvateil, destroying his/her mind and leaving him/her as a vegetable.

This is why the Dive Machine operators have to monitor closely the wave motions and levels during the Dive, as if a Critical Down occurs, they will instantly force a shutdown in the Dive Machine to stop the Dive and save the Diver.