LOL - If there is a medical explanation for it, that'll be embraced by many, including me.
However, I have a different theory: Bozo lacks a good night's sleep, so "Strike 1" from the get-go; but, I think he's also just bored as he listens to others drone on regarding something that isn't about him. He's tired, bored, and impatient to get to the time when HE can begin speaking about himself again. Everything else being said in a presentation has no importance to him so he tunes out and then fades out or just listens for the mention of his name when he can nod in agreement. It's just more of his narcissism showing itself. If it ain't about him, it ain't important! 
Either way, he looks like a sleepy, bumbling old fool on the world stage, and that's OK with me.
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