I've realised why I'm so attached to my running schedule. It's a mental thing, as apparently marathon running is too. If I follow the plan, then the plan says that I'll be OK in the race. Therefore if I follow the plan, my head will be straight, and my legs will have to follow. Or something.
Having said that, the plan goes out the window today. On the hottest day of the summer I'm feeling like I'm getting a cold, I'm knackered, and it's too hot to run: pushing 40 degrees. I am juggling this week's running anyway to accommodate a long run / race on Saturday instead of Sunday, so I'll have to move today as well.