Have you ever fallen up the stairs? It happens when you're in a hurry and running up the stairs and trip and your momentum carries upwards. This is how I would describe what it's like for someone with ADD/ADHD: their mind starts processing at a high rate, and as long as they can implement those thoughts everything works fine, but when they "stumble" - in Zach's situation, maybe because he doubts himself on a given play as an example - the mind "trips over itself" and the mental processing breaks down. This in turn can lead to more self doubt and more "stumbling". Again, I'm not a doctor or psychiatrist, nor am I privy to any discussions with Zach around this possible issue, but it really makes a lot of sense to me in light of what I saw happen to him.