I'm 5*ing this because it's a fine book. 
 I'm warning you that you might not like it because it is more literary than most fantasy you're likely to pick up. Yes, many fantasy readers read literary fiction. But also many don't. Consider yourself warned. 
 Consider the books Nausea by Jean-Paul Satre and The Girl With All The Gifts by MR Carey. This book could be the ... I won't say love-child ... let's say 'biological consequence of an abusive tryst'. 
 As it starts out you could be mistaken for believing you're going to get a high octane end-of-the-world novel with zombie analogues. Actually while it could easily have gone that way it turns more toward the navel-gazing, deconstruction of personality, relationships and society. But it's very well done. 
 Since the basics of the setup are delivered almost immediately and hinted at by title and cover I don't think I will be spoiling anything to reveal that sleep plays a large role here, and specifically lack of sleep. A rather vicious strain of insomnia unravels things and this encourages all of the aforementioned observation of the collective belly-button. 
 However, the ideas are exciting and very well written. The book kept me entertained, thinking hard, appalled, and fascinated. 
 In the end the mysteries are essentially left unraveled, which may upset some readers, but if they were to step back and try to imagine any denouement that would have satisfied them they might admit that none would and so Barnes was right not to try. 
 I would encourage you to give the book a read, bearing in mind what I've said. 
 The book ends with a poignant footnote/essay where the author shares that around the same time that the book came out he was diagnosed with a terminal and swift-acting cancer of the brain. He draws a number of parallels between what has happened to him during his treatment and the issues addressed in the book. The book has many profound things to say about life, and ultimately death. The author didn't know that a year after writing these things his life would take a turn that would throw those issues into such sharp focus. 
 In many ways it shouldn't matter. Critics are often aimed at the 'death of the author' school of criticism. But to me it mattered, and made the book, which was already personal, even more so. 
 Join my 3-emails-a-year newsletter #prizes