What is discouragement?

Over the last few weeks I've felt alive and raring to go over a new goal/project/life change that I had been anticipating. I spent night & day researching this new area of interest pouring over the Internet, dreaming about the future and imagining every nook & detail about everything it would involve. Then two days ago I received an email from a joint partner in this project indicating that I wasn't showing enough enthusiasm or commitment to this life-changing endeavour, after struggling through my emotional response for two days I came to a point of emotional collapse about it all today, I had no feeling, emotion or desire to continue at all. What had happened and how did something which had set me on fire draw a complete blank the next day?