Now that I think about what happened to me on the ride Saturday, I'm pretty sure what happened was the lack of eating proper foods after my two workouts the previous training day that did it. In the morning I had LT interval sessions and then a 4 hour recovery period (working) and back into the gym. After the initial workout I should have had a meal higher in the carb content and another higher carb meal after weight training. I did drink a recovery drink after both sessions - but timing the right meal within the magic hour of glycogen replacement is critical for long term endurance training.
Call me crazy but this shit is super fascinating.
And I think the "bonk" that I felt isn't necessarily a bad thing. It's my body reacting to after using up my glycogen levels and dipping into body fat reserves. Which is a good thing - but everybody handles this shift differently. I've found I have a low tolerance to this change - and mentally need to focus on pushing through the lows. This might be a crazy theory - but some people like the Kristin Armstrongs and cycling goddesses who seem like they are from out of this world - have an amazing natural ability to do this without having to focus on it. The rest of us struggle and, if we're lucky, adapt to this change.