No matter what, you want to be courteous. Of course, most employers want to discourage abusing sick days. It's important to remember that it's called work. It's not called f-u-n. It's nice to be able to merge the two, but the bottom line is, you're getting paid to work. So, you need to behave in a professional manner. Familiarize yourself with your company's sick-day policy and follow it.