assumming the husbandry is fine, I would chalk it up to the snake hitting sexual maturity and this being breeding season for colubrids.
those who are not familiar with that type of kingsnake...they will eat themselves into obesity and refusing food is NOT normal save for the circumstance I just mentioned.
A boa, ball python or other boid not wanting to eat for periods is normal, its not normal for a kingsnake, cornsnake or most other colubrids, save for brumation and breeding
Most snake experts do not see it as necessary at all and the rational for it can be easily dealt with. Don't feel pressured to feed your snake in a separate cage.
ditto this btw.
edit, missed the last post som'how?? Needs to see a vet and have husbandry assessed. Respirtory problems are from being too cold.