Life After Full-time Work Blog

Learn about preparing for life after full-time work through posts from Don's upcoming book.

#154 What You Need To Know About Sleep

It’s the most important ingredient in health


As I work on different projects, they often lead to blog posts. After some technical ones on investment uncertainty and longevity uncertainty, let’s switch to something far less technical. This is Part 1 of a two-parter on sleep.


For another of my projects, I imagine myself writing notes to people in different stages of their lives. One is to someone who has just finished school, ready to start out on their own life. Included is this extract:

“I’m going to give you an unusual piece of advice: sleep!

“Your health will be important through your whole life, and you’ll lay the foundations now. Sleep and exercise are the two important components that you have control over. Frankly, unless you spend all your time looking at your screen (yes, I see you smile!), you’ll probably get all the exercise you need in these next years just living your life. But I’ll bet that getting enough sleep will be an obstacle to all your exploration of life. And yet sleep is the single most important ingredient in health.

“Hey, you’re young, and it’s inevitable that you’ll deprive yourself of sleep, from time to time. That goes with the territory. We’ve all been guilty of that. I’m just saying: sleep is more important than you can imagine.”

Here’s the background.


We don’t just sleep and wake up. Every night we go through cycles of sleep, and each cycle has four stages.

The oddest stage to observe is the fourth and final one, characterized by rapid eye movements, the initials of which give it its name, REM sleep. It’s so odd that all the other stages are grouped together as Non-REM sleep, or just N for short. So the four stages are called N1, N2, N3 and REM.

N1 is when we doze off. It’s short, a few minutes. We often aren’t aware that we’re asleep. The brain and the body slow down, in transition to N2.

N2 brings light sleep, with our body subdued and its temperature dropping. Eye movement stops, and the brain’s activity slows, but with occasional short intense bursts. It lasts from 10 to 25 minutes in the first cycle, lengthening in successive cycles.

N3 is typically called deep sleep. The body slows down even more. Our muscles are so relaxed it’s tough to wake us up. And our brain moves in slow and deep waves (“delta waves”), and it’s believed that this is when the brain flushes out toxic waste that has gathered during the day. We’re groggy if woken up in this stage.

REM sleep appears at the end of the first cycle, typically starting after about 90 minutes. And it’s crucial for restoring our body and helping it to grow. Lots of brain activity here, causing not only rapid eye movements (reflecting intense, vivid dreaming) but also faster breathing, a faster heart rate and raised blood pressure; and the body becomes partially paralyzed, otherwise we’d be acting out our dreams.

N3 and REM sleep are believed to be the stages that contribute to learning, creativity and memory. That makes sense. These are the stages when the day’s activities and thoughts are mixed together and sorted out. That mixing reveals itself in dreams that may have no logic, with things coming together that aren’t possible. It also reveals itself (in my case, sometimes in the shower the next morning) as a connection across ideas that the conscious logical awake mind would never put together: hence insights and creativity. And memory comes from the experiences being moved to various regions of the brain where different aspects of them are stored.

It’s interesting that after the first one, the cycles don’t repeat in exactly the same way. We may not encounter N1 again; or if we do, it might be in the middle of the night, and we might wake up (as indeed has been the human habit for most of history – today’s notion of a single continuous sleep every night is a recent one, dating from the industrial revolution). N2 tends to lengthen over successive cycles; in fact over the whole night’s sleep we’re probably in N2 half the time. N3 is at its longest in the first cycle. REM sleep lasts about 10 minutes the first time round, and then gets longer in each successive cycle, sometimes reaching an hour.

We tend to need at least four or five sleep cycles a night.

Age has an effect too. Young children often spend more time in REM than in the other stages put together. This declines in adolescence, and then much more as we become elderly.


That’s the background. Next time I’ll tell you what hurts sleep, and how we can improve our sleep patterns.



Sleep is crucial to our health. It flushes out the waste from our day’s brain activity. It contributes to learning, creativity and memory. And it restores our body and helps it to grow.


I have written about retirement planning before and some of that material also relates to topics or issues that are being discussed here. Where relevant I draw on material from three sources: The Retirement Plan Solution (co-authored with Bob Collie and Matt Smith, published by John Wiley & Sons, Inc., 2009), my foreword to Someday Rich (by Timothy Noonan and Matt Smith, also published by Wiley, 2012), and my occasional column The Art of Investment in the FT Money supplement of The Financial Times, published in the UK. I am grateful to the other authors and to The Financial Times for permission to use the material here.

4 Responses to “#154 What You Need To Know About Sleep”

  1. David Scott says:

    Hi Don, Thank you for your post today as it was a good refresher on the topic for me. A fascinating book on the subject of sleep, which it sounds like you have already read, is “Why We Sleep” by Matthew Walker. In it he takes a deep dive into this subject.
    Thank you again and I look forward to your part 2 on sleep.

    • Don Ezra says:

      Thanks, David. Yes, for me that’s the best book I’ve ever read on the subject, and one of the inspirations for this post. I should have mentioned it explicitly.

  2. Cindy Deere says:

    Hi Don, I love that you mix this kind of discussion in with investment advice! Keep it coming!

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