Down in the dumps

SULLEN

This mood often follows disappointment and starts with a gloomy expression.

The clue "Down in the dumps" hints at a word meaning gloomy or depressed. "Sullen" fits because it describes a moody, unhappy state, matching the idea of being emotionally low. The phrase "in the dumps" is a common expression for sadness, reinforcing the connection to the answer. No wordplay is involved—it’s a straightforward definition.