瞬间心情不好了英语怎么说

"Bad mood" 可以用 "in a bad mood" 或 "feeling down" 来表示。
"In a bad mood" 是用来描述一个人当前的心情状态，指的是这个人正处于一种不好的情绪中。例如：
"I'm in a bad mood today, so I don't want to talk to anyone."
"She's been in a bad mood all week, I don't know what's wrong with her."
"Feeling down" 是用来表示一个人的情绪不好，但不一定是指一种特定的情绪，可能是多种情绪的综合。例如：
"I'm feeling down today, I think I just need some rest."
"He's been feeling down lately, I think he needs to talk to someone about it."