Why is one nostril always blocked?

It would appear milkshake has no restorative or curative properties, and I am destined to spend the day sniffing and blowing.

I'm puzzled to know why at night, one nostril is always clear? It's as though there is a tilt switch of solid mucous that tips from one side to the other as I move in bed, and is so congealed that neither dribbles down my face, nor the back of me throat. Why does it not just glue my whole nose shut, or trickle away to nothing?

Even as I type, one side is still obstructed. I can blow it clear, but I know that it will only provide temporary release, and in a few minutes that side, (or the other if I tilt my head slightly) will again be useless.

Balls