Well, I guess yesterday was a bit of a wobble, but I later got talking to someone who's done loads of the things and he gave me some words of great wisdom about doing the run.
He said - just do it.
Which seemed better than any of my reasons not to do it.
He reckons as long as I can run 10 miles I should be OK. Not 8, that's not enough, and 7 won't get me off the starting line.

But I didn't go running this morning as I was tired. I have heard that the best thing if you're feeling tired is to do some exercise cos it gives you energy - how does that work? Do you not use up all your energy when you take exercise? Isn't that the point, to prevent excess energy being stored as unsightly fat?

And another annoying thing/myth about running: there are all these inspirational stories of people who take up running, start with 5 mins, end up running the marathon des sables all because they get this endorphin high from exercise. I'd like some of that please.