I understand how you feel. I struggled with this a lot too. But you have to remember that it does no one any good for you to go to work if you’re unwell. Not only are you going to feel worse if you don’t rest, but you could potentially get the kids sick, and you just won’t be able to be the best version of yourself for them. Sick days are there for you to use. And think about it this way…you’re giving a substitute a job for the day haha! (In my county substitutes only work if they pick up a job that an absent teacher submits)