A great mystery of the universe.

So, I have a cold. Which isn’t that surprising seeing as I live in England and it is usually cold and wet most of the time. 

My question to everyone who is cleverer than me is why, I am able to breathe perfectly normally throughout the whole day until it starts creeping into evening time? Because, by the time I get to sleeping, my nose sucks at working and if air is able to get in it makes a noise which keeps me awake just as much as the lack of oxygen, so then its the revert to breathing through the mouth which keeps me awake because that’s thirsty business and really rather uncomfortable. 

So, why is this not a 24 hour problem? I’m glad I don’t have to breathe through my mouth for days on end but still? Why does this only happen when I am trying to sleep?