snore loudly, very, extremely
齁 centers on loud snoring, with the extended sense of something being very or extremely something, likely from the intensity of the snoring.
齁 combines 鼻 (nose) with 句, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to nasal sounds.
The nose 鼻 is making a loud sound like a bent phrase 句: imagine a nose snoring so loudly it forms a visible speech bubble.
For コウ, picture a nose snoring so loudly it sounds like a deep cough: cough -> コウ, and the snoring is extremely loud.