Dear Mr. Li,
I'm afraid I can't go to school today. I've had a headache and a cough. I didn't sleep well last night. This morning I felt even worse, so I had to go to the hospital. The doctor told me to have a good rest, or it would get serious. So I would like to stay in bed for two days. I hope I will get well and go back to school as soon as possible. Thank you.