His mood has been really low since he failed the exam.
Tips
usage
低迷 is the go-to word in Chinese business news for describing a weak market or economy — 市场低迷 (shìchǎng dīmí), 股市低迷 (gǔshì dīmí). It can also describe a person's mood, but 情绪低落 (qíngxù dīluò) is more common for that.