Refers to one's mental state, mood, or emotional disposition. Often used in expressions like 心気を養う (nurture one's mind) or 心気が沈む (feel depressed).
Lately, I tend to feel down.
fretfulness; irritation; tedium
Describes a state of being fretful, irritated, or feeling that something is tedious. Often used in the phrase 辛気臭い (しんきくさい) meaning 'irritatingly tedious' or 'fretful'. The kanji 辛気 is especially associated with this sense.
Reading is good for nurturing one's mind.
Listening to his complaints is irritatingly tedious.
The long wait made me increasingly fretful.
hypochondria
Standard kanji form for the general mentality/mood sense.
Used especially for the fretfulness/irritation sense.
心気 combines 心 (heart/mind) and 気 (spirit/energy), referring to one's mental state. 辛気 uses 辛 (bitter/painful) to emphasize the fretful, irritating aspect. The exact historical derivation is uncertain, but the spellings are conventionally associated with these meanings.