probably were forgetting that the 5K run yesterday was actually considerably faster than what you have generally been doing in the few days you have been back running again. Even though the 10 miles today didn't feel so good, the splits looked pretty even, taking into account the two hills. Just give it a couple of more months of steady training without additional injuries and you will undoubtedly again be running enough faster on the day after a (faster) 5K time trial so that it will still feel pretty hard--but the speed may be enough higher so that you will feel happier with the result!
Did you try eating? sounds like a bit of a bonk.
you should have come to Rhonda's Yoga class this morning, I am sure she offered.
No matter what age or gender anyone can turn being a back sufferer into a yoga believer. Talking from personal experience here, and not doing it enough by being lazy.
Note: this has nothing to do with what happened on your run today. I just felt like writing that, I am sure you had tons of advice on your back from friends since your back started to hurt.
Actually the back is slowly but steadily getting better. It helps not doing the usual falls on ventures into the woods. It helps not playing any golf since mid-July. And it also helps doing my core exercises, about 20 minutes worth every other day, for the lower back and abs. So I am trying to avoid bad stuff and do some good stuff, and for now that seems to be working.
For the most part I don't notice it at all running, but staying on the roads is part of the plan.
As far as today's run, ah well, just another life experience. Felt a bit like a bonk coming on, but a true bonk would have had me walking a lot just to get home. I'm sure, as Eric says, yesterday's effort had an impact, because until I get in better shape I just have less in the way of reserves.
On the other hand, it was still a good week of training, no doubt about that. And from the perspective of three months ago, back then I wouldn't have figured I would have any more days ever where I felt as strong and as fast as I did today... :-)