Well done on the first day of training Chilli, I am still sorting out my plan, which looks like it will be 20 weeks starting in the new year.
Did my little run/walk again tonight, its beginning to feel easier, then a hour of pilates, which was hard work as the church hall had the heating on full blast. I have heard of hot yoga but not hot pilates.
Razor sometimes runs like that just happen, hopefully next time you do that route it will be easy, or maybe you have a bug lurking and about to be ill.