Most of the fevers are caused by infections(viral or bacterial) or inflammations. For the body to fight these infections/inflammations, it needs resources and these resources are normally diverted to and distributed among various bodily functions. When you rest, most of these resources can be dedicated to fighting the infections or whatever is causing the fever.
When the cause of your infection/inflammation is well known to the body (ie, your body or your ancestor’s body has handled it multiple times before) or isn’t severe, you may recover from your fever withlittle rest.
On the other hand, if your fever is caused by a newer pathogen causing a disease which isnew to your body or when your infection is severe or you are immunocompromised, you may need absolute bed restto recover with or without medical support.
Hydration
We are all aquatic organisms inside out. The sea is inside our body. All our activities require water. When you have a fever, you need more water
to fight off the infection/inflammation of one of the main resources required is water
due to the increased temperature of the skin, more water evaporates from the surface of your body
Infections and inflammations release a lot of toxins into the body. If these toxins are not diluted, these chemicals become poisonous to our own body and its cells.
So drink lots of fluids. During a fever, if you drink a particular fluid only continuously, you may vomit. So drink plain water, ORS (Oral Rehydration Solution), diluted fruit juices, dilute soups, and so on alternatively. Keep drinking these fluids until you feel better.
If your fever doesn’t subside with these two very important measures, seek medical attention.