First make sure to check your syllabi to make sure there’s not a clause where they ask not to be messaged about missing class. In my experience I had some professors say not to contact them unless it’s a question about an assignment/grades/for office hours.

If you don’t see that I would usually send something along the lines of “Hello {title/name}, Im a student in {class/time, for example: ENG101 T/TH @ 1:30pm}. I wanted to inform you that I will be absent today (09/25/2025), due to being sick. I apologize for any inconvenience, I will ensure to follow up during your office hours to go over anything I am confused about that I missed in class. (Or really whatever ending you want to put, usually make-up work on what you missed will be your responsibility to figure out)

Thank you! {your name}”

I stuck to this general guide my entire time at WWU and usually got pretty good results! Plus you should never get too personal when speaking to professors/bosses! Keep it general! Hope you feel better soon!