Acme The crisis of a disease. Old medical writers used to divide the progress of a disease into four periods: the ar-che, or beginning; the anabasis, or increase, the acme, or term of its utmost violence, and the pa-rac-me, or decline. Figuratively, the highest point of anything.

"anabasis" as a term for stage of an illness I never heard of before I remember it only from:
Xenophon: Anabasis, or March Up Country