I don't know if it helps at all, but I used to detest exercise.
For whatever reason, I finally decided to start doing it and make myself do it no matter what, X days a week. (I think it was three days at the time).
i had an elliptical and would watch the X-Files while using it..and on the days that I felt like the last thing in the world I wanted to do was exercise, i did it anyway - but I didn't put on a heart monitor or aim for any extra feats..the feat for me those days was just sticking with it...just getting on the thing and doing the 30minutes...even if i did them slowly/with little oomph - just that i was keeping up with it..that i was doing it at all.
On other days when I felt better, I might try to increase my speed/time/whatever..but on the days I felt like you describe..just doing it - that was the hurdle..
Kind of like what you did on the 9th..just doing something even if it's not everything.
And somehow, as you've read, I went from that to...a bit more neurotic about exercise
to the point that now, not only do I do so regularly, the times that I have to push myself to exercise are few...For me, it was kind of like once I sludged through and broke past the old habits, the new ones took hold; to the point that now, it would be easier for me to visit the gym twice a day, every day than to spend the week relatively inactive.
Either way, don't beat yourself up! Whatever you do for the next day or two won't negate the work you've done the other ten..like you wrote on the 9th - you knew that another day you might need the rest even more..so, maybe this is one of those rest days..and tomorrow or the next day, you come back just as strong, if not stronger!