2. You are vomiting. Let’s be honest, the last place you want to be when you are puking up your breakfast is at work. And the last thing you want your coworker to be doing while you take a bathroom break is vomiting in the next stall. It’s not hygienic and it’s a sure sign that you or someone you work with is sick. Vomiting is definitely one of the most obvious reasons to call in sick.