expression, godan verb (-gu)
be overanxious; worry needlessly
A literary idiom from a Chinese story about a water buffalo from Wu that mistook the moon for the sun and panted from imagined heat. Used to describe someone who is excessively fearful or anxious without real cause. Rare in modern conversation; mostly encountered in classical or literary contexts.
彼は失敗を恐れて呉牛月に喘ぐような状態だ。
He is so afraid of failure that he's like the Wu buffalo panting at the moon—worrying needlessly.
杞憂 is a more common Sino-Japanese term for groundless fear, while 呉牛月に喘ぐ is a rare, literary idiom with a specific animal fable origin.
From a classical Chinese fable: a water buffalo from the region of Wu (呉), accustomed to intense heat, once mistook the moon for the sun and began panting in fear of the imagined heat. The expression is used metaphorically for needless anxiety.