My spring allergies have been acting up (juniper, I think). I noticed that they are worse when:
I'm in a car
I'm trying to sleep
I'm sitting still and quiet

and better when:
I'm riding my bike
I'm doing anything active

Why? I asked the dr and she had no clue. She made up a couple theories on the spot. The best sounding one was that the increased speed of the air passing through the nasal passages meant the pollen wasn't around long enough to settle on the membranes and cause a reaction.