the.com/moodiness

means A tendency to shift between emotional states, often unpredictably, making someone hard to read or rely on in any given moment.

from Traces back to Old English 'mod,' meaning heart, mind, courage, or spirit — a much nobler word than its descendant suggests. 'Mod' covered the whole inner life: temper, disposition, feeling. Over centuries it narrowed and darkened, drifting toward 'mood' as a passing emotional weather system rather than the seat of the self. 'Moodiness' tacks on the state of being prone to those shifts — so a word that once meant something like 'the condition of having a mind' ended up meaning 'the condition of having a mind that won't sit still.'