I was wheezing a lot on the ride yesterday and I woke up this morning feeling very wheezy and my eyes were streaming. I reckon that I might be sensitive to the pollen we were exposed to riding past those fields of oil seed rape yesterday. I've never suffered from full-blown hay fever but have had this wheeziness at times in past summers.
I was chatting to TMN about this on the ride. I have just been diagnosed with asthma - after a few years of me and the asthma nurse trying to figure out what's going on - April/May last few years has been exceptionally bad. All this has happened since moving from Cambridgeshire, so probably a lot to do with change in surrounding crops etc. In Cambs oil seed rape never got to me at all (but we kept bees there - and it is well documented that eating local honey helps hayfever/pollen aggravated asthma). This year has been worse apparently - to do with the long wet period in April/May and the effect on the pollen distribution or something. May be worth a visit to your GP or if there's an asthma nurse in your local practice.