Ah, Selva is wondering about something that has also been puzzling me:

For the past few weeks I have been in sneezing hell. Everyday when I wake up, my phlegm factory wakes up with me and kicks into high gear producing copious amounts of that white jelly that dribbles out of my nose (disgusting? Imagine what I feel..It’s coming out of MY nose!) England has too many flowering plants. The damn pollen is killing me. Anyway, the question is: All the air borne irritants are present even while I sleep but I do not dribble when I sleep. Why? Why is that my nose runneth over only when am awaketh?

I, too, am afflicted with this yearly blight, this vile assault on my mucosae. Portland Anthophyta are trying to kill me; Satan has relocated his infernal Itch Factory to my nose.
On a bad (especially pollenaceous?) day, my nose and eyes begin to itch and run within moments of waking. Surely the offending gametes were present in the moments before I awoke: what part of the reaction requires consciousness? Conversely, what aspect of the sleep state prevents the physical manifestations of the allergic reaction? Now, sneezing being a reflex, it seems intuitively reasonable that it might be suppressed by sleep; although it seems less clear, itching might be a similar case¹. I’m also aware that the sinuses can produce mucus in one’s sleep, as is anyone who’s ever had a cold or ‘flu. This is different: not only does the sneezing hold off while I’m asleep, but so does the snot. I sometimes wake with blocked sinuses, but never — unlike when I have a cold — with a runny nose. Once I’m awake, though, all bets are off and I have to make a run for the drug cabinet.
I have no idea what is going on, and would be most grateful if the lazy web could tell me. (A quick google reveals nothing of any use.)

¹ Mechanism, of course, is a whole nother can of worms in both cases. Is there a neurologist in the house?