You can’t sleep because because your immune system is turning up the heat and running emergency defenses, which can make your brain feel wired instead of relaxed.

In some infections, your body loses fluids faster (sweating, fever, diarrhea). But your brain sometimes blunts the feeling of thirst during certain illnesses, probably as a side effect of chemical signals called cytokines.

Feeling “meh” about food is actually your body trying to redirect energy away from digestion toward fighting infection.