Last year, in early June, I visited Sweden. Tree pollen levels were very high - you could see the pollens covering every water surface (many of those in Sweden).
My asthma reacted to something quite badly, especially at night. I don't normally have hay fever, though I have had some occasional, very occasional suggestions I can react in that way, in some combinations of circumstances.
Can you get asthma with pollen without having hay fever symptoms? That was what seemed to happen to me last year. This year I want to be better prepared, thus the question.