Burnt out. People say it about a hard week, a bad month, a job they dislike, and about something much more serious.
It does have a definition.
Sources
World Health Organization, 28 May 2019 — Burn-out an occupational phenomenon: International Classification of Diseases. The three dimensions, the attribution to chronic workplace stress, the restriction to the occupational context, and the explicit statement that it is not classified as a medical condition