I had a wonderful run a few Sundays ago (well, wonderful for my middle-aged self), rolled home feeling great, then woke up in the middle of the night with a hot raw patch in the top of my mouth and a couple of days of misery coming on.

But I suspect it wasn't the cold coming on that did for me, on the one hand, more likely exposure to somebody with a new and improved bug a day or so before. And on the other hand, I'm not sure that co-workers who got to listen to me cough would have considered the run worth it.