I’ve read several books​ ​about​ ​sleep recently,​ ​and​ ​their​ ​authors​ ​all​ ​tell​ ​me​ ​the same​ ​three​ ​things.​ ​The​ ​first​ ​is​ ​that,​ ​in​ ​the modern​ ​world,​ ​it’s​ ​hard​ ​to​ ​get​ ​enough sleep.​ ​The​ ​second​ ​is​ ​that​ ​sleep​ ​is​ ​very important.​ ​Every​ ​night,​ ​we​ ​pass​ ​out.​ ​Every morning,​ ​we​ ​regain​ ​consciousness, half aware​ ​that​ ​time​ ​has​ ​passed.​ ​For​ ​a moment,​ ​we​ ​might​ ​have​ ​the​ ​impression we’ve​ ​just​ ​been​ ​flying​ ​through​ ​the​ ​air,​ ​or that​ ​we’re​ ​about​ ​to​ ​be​ ​executed.​ ​The whole​ ​thing​ ​is​ ​totally​ ​weird.​ ​That’s​ ​the​ ​third thing.

Before​ ​I​ ​get​ ​into​ ​the​ ​weirdness,​ ​I’ll​ ​say something​ ​about​ ​the​ ​importance​ ​of​ ​sleep. Authors​ ​tend​ ​to​ ​think​ ​that​ ​what​ ​they’re writing​ ​about​ ​is​ ​important.​ ​But​ ​sleep authors​ ​are​ ​a​ ​breed​ ​apart.​ ​They’re​ ​like sleep​ ​salesmen.​ ​And​ ​I’ve​ ​never​ ​come across​ ​a​ ​sleep​ ​salesman​ ​quite​ ​as dedicated​ ​as​ ​Matthew​ ​Walker.​ ​An Englishman,​ ​he​ ​is​ ​the​ ​director​ ​of​ ​the sleep​ ​and​ ​neuroimaging​ ​laboratory​ ​at the​ ​University​ ​of​ ​California,​ ​Berkeley.​ ​‘I am​ ​in​ ​love​ ​with​ ​sleep,’​ ​he​ ​tells​ ​us.​ ​‘I​ ​am​ ​in love​ ​with​ ​everything​ ​sleep​ ​is​ ​and​ ​does.’

So:​ ​what​ ​is​ ​sleep?​ ​Well,​ ​it’s​ ​not​ ​‘the absence​ ​of​ ​wakefulness’​. It’s​ ​the presence​ ​of​ ​something, ​a​ ​different​ ​state​ ​— one ​that​ ​heals​ ​you,​ ​increases​ ​your lifespan,​ ​helps​ ​you​ ​to​ ​look​ ​slim​ ​and​ ​toned, makes​ ​you​ ​brighter​ ​and​ ​more​ ​charming, more​ ​attractive,​ ​sharper,​ ​better​ ​at​ ​maths and​ ​spelling,​ ​better​ ​at​ ​driving.​ ​I​ ​could​ ​go on​ ​for​ ​ages​.​ ​Walker​ ​tells​ ​you,​ ​over and​ ​over,​ ​of​ ​the​ ​benefits​ ​of​ ​sleep.​ ​Reading late​ ​at​ ​night,​ ​I​ ​turned​ ​the​ ​pages, fascinated,​ ​hour after​ ​hour.​ ​I​ ​kept​ ​wanting to​ ​go​ ​to​ ​sleep.​ ​But​ ​not​ ​because​ ​the​ ​book is​ ​dull.​ ​It’s​ ​like​ ​reading​ ​about​ ​the​ ​joy​ ​of swimming,​ ​and​ ​wanting​ ​to​ ​jump​ ​into​ ​a lake.

It’s​ ​not​ ​just​ ​that​ ​sleep​ ​is​ ​good.​ ​It’s​ ​that​ ​not sleeping​ ​—​ ​or​ ​even​ ​not​ ​sleeping​ ​for​ ​the​ ​full eight​ ​hours​ ​—​ ​can​ ​be​ ​terrible.​ ​I​ ​knew​ ​that five​ ​or​ ​six​ ​hours​ ​wasn’t​ ​great.​ ​Walker​ ​tells us​ ​just​ ​how​ ​bad​ ​it​ ​can​ ​be.​ ​What’s​ ​the worst​ ​sickness​ ​you​ ​can​ ​think​ ​of?​ ​Well,​ ​not sleeping​ ​enough​ ​might​ ​give​ ​you​ ​that​ ​very sickness.​ ​Sleeping​ ​too​ ​little,​ ​for​ ​instance, ruins​ ​your​ ​immune​ ​system.​ ​Walker​ ​cites an​ ​experiment​ ​in​ ​which​ ​people​ ​had​ ​a​ ​virus sprayed​ ​up​ ​their​ ​noses;​ ​people​ ​who​ ​got​ ​a good​ ​night’s​ ​rest​ ​were​ ​much​ ​less​ ​likely​ ​to be​ ​laid​ ​low.

Not​ ​sleeping​ ​enough,​ ​Walker​ ​tells​ ​us,​ ​can lead​ ​to​ ​many​ ​conditions:​ ​‘Alzheimer’s disease,​ ​anxiety,​ ​depression,​ ​bipolar disorder,​ ​suicide,​ ​stroke ​and​ ​chronic pain.’​ ​Also:​ ​‘cancer,​ ​diabetes,​ ​infertility…’ But​ ​he​ ​doesn’t​ ​just​ ​list​ ​these​ ​horrors.​ ​He explains,​ ​at​ ​length,​ ​how​ ​sleep​ ​wards​ ​them off.​ ​For​ ​instance,​ ​if​ ​you​ ​imagine​ ​your​ ​brain as​ ​a​ ​city,​ ​it​ ​has​ ​a​ ​sort​ ​of​ ​sewage​ ​network. When​ ​you​ ​use​ ​your​ ​brain​ ​to​ ​think,​ ​your brain​ ​cells​ ​emanate​ ​waste​ ​matter.​ ​When you​ ​sleep,​ ​your​ ​brain​ ​gets​ ​a​ ​‘power cleanse’​ ​—​ ​some​ ​of​ ​the​ ​cells​ ​shrink, allowing​ ​cerebrospinal​ ​fluid​ ​to​ ​flush​ ​out the​ ​debris.​ ​Some​ ​of​ ​this​ ​debris​ ​is​ ​the​ ​type of​ ​protein​ ​that​ ​causes​ ​Alzheimer’s disease.​ ​‘Parenthetically,​ ​and unscientifically,’​ ​says​ ​Walker,​ ​he​ ​can​ ​think of​ ​two​ ​famous​ ​sleep-dodgers.​ ​Ronald Reagan​ ​and​ ​Margaret​ ​Thatcher.​ ​Maybe their​ ​sewage​ ​systems​ ​backed​ ​up.

Every​ ​animal​ ​sleeps.​ ​Insects​ ​sleep. Dinosaurs​ ​slept.​ ​Dolphins​ ​sleep​ ​by switching​ ​off​ ​half​ ​their​ ​brains,​ ​and​ ​then​ ​the other​ ​half,​ ​but​ ​never​ ​both​ ​at​ ​once.​ ​Sleep, we​ ​keep​ ​thinking,​ ​is​ ​not​ ​about​ ​doing nothing.​ ​It’s​ ​like​ ​taking​ ​your​ ​car​ ​for​ ​a service.​ ​Every​ ​part​ ​of​ ​you​ ​is​ ​spruced​ ​up. And​ ​dreams​ ​are​ ​extremely​ ​important. Dreams​ ​enable​ ​you​ ​to​ ​make​ ​creative connections.​ ​Incidentally,​ ​you​ ​dream​ ​more as​ ​the​ ​night​ ​goes​ ​on.​ ​So​ ​if​ ​you​ ​only​ ​have six​ ​hours,​ ​your​ ​creativity​ ​will​ ​suffer.

When​ ​you​ ​dream,​ ​the​ ​connection​ ​is​ ​cut between​ ​your​ ​brain​ ​and​ ​your​ ​muscles,​ ​so you’re​ ​temporarily​ ​paralysed.​ ​This​ ​stops you​ ​from​ ​thrashing​ ​around.​ ​Meanwhile, your​ ​eyes​ ​roll​ ​around​ ​in​ ​their​ ​sockets.​ ​If you​ ​suffer​ ​from​ ​PTSD,​ ​your​ ​brain​ ​might​ ​be trying​ ​to​ ​process​ ​the​ ​bad​ ​memories;​ ​if​ ​it fails,​ ​it​ ​might​ ​try​ ​again​ ​the​ ​next​ ​night. Hence​ ​recurring​ ​nightmares,​ ​which​ ​might ruin​ ​your​ ​sleep.​ ​Walker​ ​tells​ ​us​ ​about​ ​his research​ ​into​ ​recurring​ ​nightmares;​ ​
it’s fascinating.

As​ ​is​ ​the​ ​whole​ ​of​ ​this​ ​book.​ ​Is​ ​there​ ​a better​ ​book​ ​about​ ​sleep?​ ​I​ ​doubt​ ​it.​ ​He tells​ ​us​ ​about​ ​hundreds​ ​of​ ​other​ ​things​ ​— ‘microsleeps’,​ ​falling​ ​asleep​ ​at​ ​the​ ​wheel, the​ ​way​ ​light​ ​and​ ​screens​ ​trick​ ​our​ ​body clocks,​ ​so​ ​we​ ​stay​ ​awake​ ​too​ ​long.​ ​And the​ ​less​ ​we​ ​sleep,​ ​the​ ​shorter​ ​our​ ​lives are.​ ​Yes,​ ​I​ ​thought,​ ​as​ ​I​ ​finished​ ​this​ ​book, sleep​ ​is​ ​hugely​ ​underrated.​ ​Then​ ​I​ ​looked at​ ​the​ ​clock.​ ​Could​ ​that​ ​really​ ​be​ ​the​ ​time?