When I was in college, during my senior year, I was studying a lot and staying up late getting ready for final exams. I was also working part time and doing the other stuff that college kids do. Basically, I wasn't getting much rest.
About half way through finals I got sick. I caught a cold. At first I just felt tired and didn't have much energy. Thankfully, I was able to get through that final week without having to miss any exams.
That following week I got really sick, but I put off going to the doctor because I was so busy moving and getting ready to start a new job. By the time I finally went to the doctor, I had a terrible cough that was keeping me awake, and I was pretty weak.
I went to the doctor and the nurse gave me a shot of penicillin (I think it was penicillin.) Anyway, part of the problem was bronchitis, and the symptoms were rough. Once I started taking the antibiotics, I started feeling better in a few days.