An unwell person isn't feeling their best - they might be sick or tired.
You hear people say "I'm not doing so well" or "I've been feeling unwell lately." This usually means they're experiencing some physical discomfort, like a headache, stomachache, or fatigue. It's common to use this phrase when you're not up for work or school because of illness, or when you need to take it easy for a bit.
Not in good health; not feeling well; somewhat ill
Example: feel unwell
