Formal:
* मुझे ठीक नहीं लग रहा है (mujhe theek nahin lag raha hai) - This is a general and polite way to say you're not feeling well.
* मैं बीमार हूँ (main beemar hoon) - This means "I am sick" and is more direct.
Informal:
* मैं थका हुआ हूँ (main thaka hua hoon) - This means "I am tired" and could be used if you are feeling fatigued.
* मेरा पेट खराब है (mera pet kharab hai) - This means "My stomach is upset" and is specific to stomach problems.
* मुझे बुरा लग रहा है (mujhe bura lag raha hai) - This means "I am feeling bad" and is a more casual way of saying you're not feeling well.
If you're feeling really sick, you might say:
* मैं बहुत बीमार हूँ (main bahut beemar hoon) - This means "I am very sick".
It's important to note that the best way to say "I'm not feeling well" in Hindi will depend on the situation and your relationship with the person you are talking to.