I know it can be hard to take a sick day b/c they all want to know what is wrong with you.If it's cold and flu season then it's easy to think of something.

You could also say you have a bladder infection, actually at the start of my outbreaks it feels like a bladder infection.

Or tell them you have eaten something that didn't agree with you.

If you have children you can say one of them is sick and no one should ask any questions.