I can relate to all the posters, especially the OP. It seemed to me a whole different approach to riding english skills "back then". My trainer, who I've had for 3 years, is so methodical in her approach, and what I observed was so much attention to technical detail. When I first began my impression was of being so over whelmed with instruction. Really, only 2-4 things at a time can be addressed in the beginning. After a while I could keep several things going at once, which makes me feel pretty good about my learning.
I would also say, you weren't "that" out of shape. I run, lift weights, and do yoga and still found my core wasn't entirely ready for the positional demands, nor my fitness level for riding. It's very specific to riding. Now of course its a different story, as you also experienced. The one biggest thing I noticed was that after riding 4+ times a week for several weeks my muffin top disappeared. Yay!