Jerry A runners blog-updated daily
Self anointed title
Last night I had a 20 mile run scheduled. I'd prepared for it, thought I was well up for it and then on the way home from work just came to the conclusion that I wasn't feeling good and I decided not to go.
Good decision. Most likely is that it was a combination of the factors that you mentioned. In particular the large lunch could have caused a drop in your energy levels as all energy went to help out your digestive system!