That's usually going to be a 12 or 13 class semester, though, so if you're missing 2 classes, that's like 15% of the class time. And the grade reduction isn't that big a deal, really; it's a penalty, but it won't stop you passing the course if you're showing up and doing the work.
Your grades really don't matter nearly as much as people think, in college. Case in point; I got a 0.82 GPA in my first year. I got better, earned a BA w/ honours, got my B. Ed., and now because the teaching industry is glutted and full-time work is hard to find, I'm going back to do an MA next year.
That 0.82 in my first year hasn't kept me from advancing my education. And it's not like employers ask to see a transcript; they typically just want proof of graduation. Your grades become really important for things like maintaining a scholarship, but if you're on a scholarship, you really shouldn't be skipping. And if you're going to miss like half the course due to serious illness, you should be withdrawing, so it doesn't count against you.