@JackHuncho I'm not an expert on the matter, but what Nakami describes as the reason for his insomnia is basically clinical depression. Not that I actually have clinical depression but I went through some depresive episodes on the past and a friend of mine does atually have, and what Nakami describes is basically how I felt some time ago and what my friend is going through right now: the lose of purpose and hope, more than sadness itself. It reminded me to an interview I saw some time ago with a guy who has an schizofrenic disorder and other mental disorders including depression, where he was asked how he felt about the future and his answer was pretty similar to what Nakami tried to explain (not saying he is schizofrenic or something lol). Here's the interview and his answer if you wanna hear it, it may be kind of a stretch to you question but I still think it's interesting (and may I say, devastating), so it's worth the watch: https://youtu.be/GU8VmJsX6-s?t=663
Dunno if I'm explaining myself right haha, but at least that's what I got from this chapter uwu
And sorry if my english is a little weird too