Sure. I'll start by prefacing that I'm not necessarily wholly attributing these as faults of Walker's book. I don't doubt I have a higher propensity for certain anxious responses, or perhaps my personality made me more susceptible to the sort of thinking I'll discuss.
Walker's book—and his accompanying Ted talks and podcasts—instilled a deep sense of sleep anxiety in me, which led to episodes of chronic insomnia (still occurs today). I had never experienced these issues before reading the book. Unfortunately, his message ensures that the insomnia is self-exacerbating, causing a vicious cycle.
Essentially, I find it very wrong for Walker to focus on and overhype the negative aspects of sleep loss as much as he does. Guzey's article [0], also linked above, goes through much of this. Why We Sleep turns into a horror book if you aren't able to sleep for whatever reason. It implies that, from just one bad night's sleep,
1. your immune system will deteriorate significantly
2. the chance that you develop a cancer will increase
3. your mental health will suffer
4. you are more likely to develop anxiety or depression
5. the probability you hurt yourself will increase
6. your mental faculties will be destroyed, you will be unable to reason well
7. you are at higher risk of mortality (!)
8. you are literally closer to death, which the book supports by mentioning fatal familial insomnia (FFI)... a flawed analogy
... and much more.
I was initially ok after reading the book, but the problems really started after I had a bad nights' sleep. I was absolutely terrified the following night, remembering all the awful things that will happen to my body and mind if I do not recuperate the next night. And we all know how easy it is to lose sleep when you are worried. I stayed up until 6 AM that night. Every passing hour made it harder to sleep.
Naturally, this started a cycle. Grumpy and even more anxious the next day ("two days? wow, am I now DOUBLE the chance of cancer and depression?"), sleep began evading me more and more often. The bed became a place of anxiety. Every minute I spent awake, I remembered Walker's book and the terrible things he told me was happening to my body due to the insomnia. This caused an infernal, unending loop of insomnia. Morning birdsong became hell to my ears.
I still sometimes suffer from it to this day, but Guzey's essay really helped. I think some quotes can do my point more justice:
> Your essay on Why we sleep - I can’t thank you enough. I’m a sleep doctor in Oregon and have seen many many patients who have developed severe sleep anxiety and insomnia. Two friends in the sleep field and myself weekly have talked about people that slept well until reading this book.
> I wanted to drop you a line to thank you for all the time and effort involved in debunking Matthew Walker’s book. As someone who works with individuals with insomnia on a daily basis, I know from firsthand experience the harm that Walker’s book is causing. I have many stories of people who slept well on less than eight hours of sleep, read Walker’s book, tried to get more sleep and this led to more time awake, frustration, worry, sleep-related anxiety, and insomnia.
> My patients are coming to me after reading this alarmist book, with insomnia that they did not have before, and worse, harder to treat because although the book has caused these anxieties - they can’t shake their newly built alarmist beliefs they learnt from the very same book.
> Scott slept well his entire life until he listened to a podcast that led him to worry about how much sleep he was getting and the health consequences of insufficient sleep. That night, Scott had a terrible night of sleep and this triggered a vicious cycle of ever-increasing worry about sleep and increasingly worse sleep that lasted for ten months.
[0]: https://guzey.com/books/why-we-sleep