Kudos for persistence. Maybe stress, but also weather? 90° in where are you, Buffalo? (I used to buy goalie gear there, so I associate it with COOL; I have relatives in Bergen.) With me, it's always a while to acclimate - kicks my butt, I get headaches, even training in the cooler cellar, lots of heavy breathing during training of late and I've temporarily dropped extra cardio. Heat is still better than snow - but yesterday I caved and unwrapped/turned on the ac!