"Falling into Madness" refers to the different levels of chaos in Vicissitudes or Vicisses, particularly defined for the latter. The order of the five different stages are Lucid, Vulnerable, Psychotic, Broken, and the Lunatic stage.
The five different stages are:
Lucid, which is the stage in which regular human mentality and physiology rests.
The Vulnerable stage begins when something disturbs a Viciss's emotional balance. This stage is not as dangerous as the next three, but the appearance of the individual begins to show physical changes, such as glowing eyes, extruded fangs, and possibly a few unnatural appendages. A major example of this stage is Annabel and Gabriel, who are known for being permanently in the Vulnerable stage. Anabel had the shortest time in incubation, and therefore has never reached the Lucid stage, as shown by her apparent wings and constant glowing eyes, although she retains a Lucid mind. Due to the torture the Men of Eden had induced on him, Gabriel permanently falls between the Vulnerable stage and the Psychotic stage in his mental state, but not quite his physical state (as it only appears when he is angered).
Psychotic stage is the stage in which the mentality of the Viciss is completely lost, but they still retain a complete human form with the exception of several beastly features.
The Broken stage is the level in which the boundary of chaos is broken.
The Lunatic stage is the fifth level, and the level in which all Vicissitudes are found on. This stage is when both consciousness and the human form is completely lost. They completely turn into a beast, without a single human attribute. Vicisses, on the other hand, generally avoid falling to this level, because at this level, it is impossible to revert back to the Lucid stage without certain conditions. If a Viciss is unable to revert back into the Lucid stage within a certain amount of time, they will permanently stay on the Lunatic stage and their physical composition will forever remain that of an actual Vicissitude (in other words, they literally become Vicissitudes at this stage). The only possible way to revert Viciss back to the Lucid stage is if they consumer the blood of the ADAM Core, which has the power to purify the chaos in their hearts. However, because of the new connection between the ADAM Core and EVE Steinway, the only way to revert them back is by consuming ADAM's blood, which flows through Eve.