Ever so slight word of caution, my reading this book coincided with a period where I wasn’t sleeping very well for various reasons, and I think the book actually made it worse as I was more worried about the detrimental effects of my poor night’s sleep due to what I’d read, so I stopped reading it! I’ve heard the same anecdotally from a couple of other people too.

That said, I think it is a very important book, and now I’ve hopefully resolved my sleep issue (with thanks to some of the comments on https://news.ycombinator.com/item?id=16671944 - primarily the advice about having a regular “sleep schedule”) I look forward to finishing it!