You're not alone WooHoo.
I 'Hit the wall' in 1997. I was on a 300km Midlands Mesh between Oakham and Lutterworth. I had completed 257 km and was on the way home. It was pissing down with rain and I was soaked through, riding against a 20 mph headwind.
I had struggled to climb a hill, freewheeled down the other side, only to be faced with another hill. I forced myself, in agony, and the next thing I knew I was lying on the grass bank with my hands holding the bars and my shoes still in the clips. 15 minutes had gone by, which I have no recollection of.
I was looking closeup at a wet pink thistle, but had absolutely no clue what it was. I thought it was an Angel.
I lay there for about half an hour before I could get on my feet.
The route changed to Leicester Railway station. Alternate 15 minutes riding and 15 minutes walking.
Since then, I have done some studying.