Flu-like symptoms develop, e.g. diarrhea, nausea, fever, confusion, dizziness, weakness, and generally feeling bad.

出现类似流感的症状，例如腹泻、恶心、发烧、头晕，虚弱，同时自我感觉很不好。

youdao

He was feeling bad. He went to work, however, and tried to concentrate.

他感觉不舒服。但他仍然去上班，并且努力集中精神工作。

《牛津词典》

Don't say anything more; she's feeling bad enough as it is.

你别说了，她心里正不好受呢！

《新英汉大辞典》

They include sleepiness, feeling sick or having bad dreams.

VOA: special.2009.04.07

Your stomach sinks, you have that sinking feeling in the pit of your stomach, when you get a bad grade on a test.

当你考试考砸的时候,你的胃会垂下去,或者说,会有胃部下垂的感觉

耶鲁公开课 - 死亡课程节选

So one of them's kind of feeling bad about something, and the other one is purposely doing bad, I think.

NPR: New Pornographers' A.C. Newman Gets 'Guilty'

But, for this one guy, I worried about his wife -- on top of feeling bad that he had to live a double life.

CNN: In the Field

The goal, as the title makes clear, is to help women around the world by empowering them, celebrating their successes, instead of feeling bad about the vast inequalities that do exist.

CNN: Africa doesn't need our 'pity'