If they ask why…. You can respond, “because I’m not. Thank you, have a good day.” CLICK
If you’re ill mentally or physically while on the job and need to go home you can say…. “I can’t finish the rest of the day and I have to leave.” When they try to guilt you because they’re under staffed or busy, remember that’s not your problem. Your health is.
If you don’t give an excuse/reason they can’t gaslight you if you say I’ll talk to you tomorrow about this matter and leave.
If you can get someone to cover your shift then that’s helpful but if you can’t don’t hold that guilt ok. Even when billy bob says he works while he’s sick. Your coworkers will be fine tomorrow even if they choose to feel any other way.