It's super important to avoid working when you're sick, not just because you feel rotten. What may be "just a cold/flu" to you may be life-threatening to a vulnerable partner or customer. I'm one of those, I'm immune compromised and a sniffle for someone else can have me down with pneumonia for a month! So please, PLEASE don't work when you're not food safe. If you can, get in touch with other partners to help cover for you. Poke around and find when others are available so you know who to call first. When I'm not sick I like making sure that my team knows that I have a flexible schedule and I am a good person to call for coverage. You will not be fired for calling out sick, and you certainly wouldn't be without first having a conversation with your SM for them to check in on you if it's a major issue. BTW you can get coverage from other stores if you're really strapped, so it's worth getting to know partners from your general area.

Well, for us, California law is that after three days you must get a doctor’s note and you should easily be excused and even use Sick pay just ask your SM. Also if you know you have something ahead of time like midterms and studying, I always get baristas calling me to cover shifts from different stores if no one else at your store could take your shift. The point your SM needs to see is that you tried to get it covered. By law, you don’t have to find coverage for yourself for an emergency like being uncontrollably sick. Feel better!! Try dietary supplements and some OJ!!:)

I mean. Midterms are midterms it's not something you can just not do.
Last month I called out and had to switch shifts or have someone cover me so often, and I wasn't fired. I always made sure my shift was covered wayyy before the day off tho. And when emergencies happened I always called other partners to see if they would take the shift or switch with me before I called out.
Try to find someone to take the hours!!! Might be hard last minute, but the worst they can say is no.
Also I doubt you'd be fired unless it was just crazy calling out but it just sounds like you're a student living during flu season!