As the body is organic and has a finite lifespan, it is subject to normal biological clocks, susceptibility to foreign body intrusion (as in the case of viruses and bacteria).
However the body is also a very intelligent vessel. It can heal itself, naturally, under normal circumstances.
Sometimes we experience pain as a warning to stop doing something..the mind is not immune to this.
A fever is an indication of an infection being fought by the body. Most other symptoms are the same. That we are used to taking medication to get away from something..is a conditioned response.