Is it normal for one nostril to block everytime I lay down?

No, but I think you should be evaluated by a nasal specialist (e.g., an "otorhinolaryngologist"--an ear, nose and throat doctor) for any abnormality.

Some people have growths (folds?) which can block the air passage; I knew someone who had some removed.

I'd say 'common', but technically not normal. it's often an issue in the spring as allergies flare up, at least for many people.

Hope this helps.

https://health.clevelandclinic.org/why-do-i-sometimes-get-stuffy-in-one-nostril

It this happens only with one nostril, either left or right, then you may have a deviated septum that reduces the air passage in that nostril and it happens most when you lie on the side where the deviated septum is.

Its your sinus & yes that is normal

Post Nasal drip

[media=https://youtu.be/xYpQncLUvbs]

Mine does it but mine will open up if I lay the other way but then the other one closes