system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why does our body react to being sick or having allergies by blocking up our main means of breathing?

Why does our body decide to potentially harm us whenever we're sick or don't agree with something around us? Isn't it not in the best interest of our body to potentially cause asphyxiation?

tl;dr: why does our body ~~inflame~~ congest our noses whenever we're sick or under the weather?

Edit: Wow! Thank you for all of your responses. I didn't expect this to blow up like it did overnight. I would be thrilled if I were a five year old!
gpt
increased mucus production is the body's way of attempting to expel the allergen/virus/bacteria by washing it into the stomach or out the nose/mouth, the latter contributing to the spread of infections

like a too-high fever, this is prioritizing removal of the invader over *everything* else, though you are actually unlikely to asphyxiate on mucus, since you dont produce enough. uncomfortable and annoying, yes, major problem, not so much.

sometimes nasal congestion is from sinus infections, where the infection plugs up the sinuses, which creates the pressure/pain you feel behind and around your eyes and nose. 

infections IN the lungs can prevent that mucus from leaving, and draw off fluid from the blood or the surroundings, which can lead to fatal breathing problems (see tuberculosis)