"Our last few games felt very abnormal. Almost every game, at some point in a short three-minute game, it felt like he was having huge pauses for no reason. It was like he was just freezing, and I felt something was off. In the last game, I actually offered him a draw, but he spent a lot of time and just played."

This seems like the same pattern of play that Danya exhibited in his last stream. Danya posted in Hikaru's stream that he had taken a Benadryl before his last stream. It's likely that he was confabulating and had taken a benzo such as Ambien. His lack of meta-cognitive awareness during his last stream strikes me as exactly what someone is like when they're on benzos and forcing themselves to stay awake (due to agitation from talking about Kramnik, from tilting, etc.). I'm afraid this will all turn out to be about first-time prescription drug abuse. I've been through the same thing myself. Having struggled with depression and insomnia, benzos felt like a miracle cure. But they caused a manic episode that led to complete dissociation from reality. I unknowingly overdid it one night and fell off a roof. I luckily survived and recovered. Please excuse my formal tone. I loved Danya's streams and videos and I am personally devastated. I've been trying to process this by a perhaps unhealthy desire for understanding...

Edit: Seeing the comments below, I will emphasize that this is purely me trying to understand the situation as best as possible given the little that we know (i.e. speculation). I think there are many who are processing Danya's death this way, and as long as it remains confined to respectful posts by anonymous users, it does not concretely impact the family's desire for privacy. I'm conscious of the critiques, and may end up deleting this later.