So I did the Day 2 workout from Couch-to-5K this evening. And it went so much better than Day 1, which is an identical workout. I mean, it wasn't enjoyable by any stretch of the imagination, but I never felt on the verge of collapsing or unable to speak. When the app told me it was time for the cool-down, I said, "Wait—what? Really?" Who knows what it was that made the difference. Given that the conditions I'll usually be jogging in will be these rather than my Day 1 conditions, this gives me some hope.