I slept for 8 hours a night and still felt exhausted — until an expert changed one simple thing about my sleep schedule

Recently, I’ve been waking up exhausted and groggy, despite sleeping for eight hours every night. I’ve checked off everything that could secretly be sabotaging my sleep: I have the best mattress for my body, I avoid late-night dinners, and I don’t snore (well, not enough for concern).

And the weirdest part is that I'm wide awake and full of energy after just 7.5 hours of sleep. How can 30 minutes make such a massive difference?

For Sleep Awareness Week 2026, I called on Dr. Lindsay Browning, a globally renowned neuroscientist and sleep expert, to ask what was going on and how I could break out of my morning funk. Here's what she told me...

Key take-aways: At a glance

• If you feel exhausted after 8 hours sleep, it's because you're waking in the middle of a sleep cycle.
• On average, a sleep cycle for healthy adults lasts around 90 minutes.
• So if you're sleeping for 8 hours, you're likely to be deep in a cycle when your alarm goes off.
• To wake up more easily, with more energy, aim for 7.5 or 9 hours sleep.
• This way, you'll wake up towards the end of a sleep cycle where you'll be in a lighter stage of sleep and therefore easier to rouse.

Why I wake up exhausted after eight hours sleep

When I explained my situation to Dr Browning, straight away she knew what was going on.

When we sleep, our rest is broken up into cycles, she told me. And these cycles are made up of different sleep stages: light sleep, deep sleep and REM.

“Approximately, every hour and a half, we’ll go through light sleep, deep sleep, back through light sleep and then have a little bit of REM sleep,” says the chartered psychologist. “And then the next sleep cycle starts.”

Dr. Browning describes each sleep cycle as “a wave” going through the stages.

“If you’re woken up from the deepest part of sleep, so the middle of a deep sleep cycle, you’ll feel really groggy,” she explains.

“You’ll feel so tired because you’ll have this thing called sleep inertia,” the doctor adds. Sleep inertia is the scientific name for waking up feeling foggy — it’s particularly common to experience it after napping.

So why do we get sleep inertia if we interrupt a sleep cycle? “Your body wants you to finish the full sleep cycle,” Dr. Browning explains.

“You can’t easily stop in the middle of a roller coaster because you have momentum, and the same thing happens with your sleep.”

So after eight hours of sleep, it’s likely I’m still in a deep sleep stage compared to the lighter stages at the beginning and end of a cycle.

“If your alarm were to go off half an hour earlier or half an hour later, it’s more likely to catch you in a lighter part of sleep, and you’d wake up in that moment and feel more awake,” explains Dr. Browning.

The simple fix? Aim for either 7.5 hours or 9 hours sleep a night instead, so that when my alarm goes off I'm waking up towards the end of a sleep cycle (when I'll naturally feel less tired and groggy) rather than deep in the middle of one.

How to battle morning brain fog and low energy

It’s all well and good knowing this, but it’s not always easy to put it into practise when our busy work and social lives dictate our sleep schedules. But here Dr. Browning shares some practical ways you can battle brain fog...

Invest in a sunrise alarm clock

“I recommend one to everyone,” says Dr. Browning of sunrise alarm clocks. These clocks wake you up gradually using a light that slowly becomes brighter and brighter.

“Even with your eyes closed, you can sense light,” says Dr. Browning. “As they brighten up, they help to pull you into a lighter part of sleep,” meaning you’re less likely to be rudely awakened in the middle of a deep sleep stage.

“And when you do wake up, there’s a really bright light there… which helps you to wake up, get rid of sleep inertia and suppress melatonin.”

The best sunrise alarm clocks allow you to customize your sunrise… including the time it takes to brighten, how bright the lamp gets and the sounds that accompany it.

Since I’ve started using the Lumie Bodyclock Shine 300, which I previously reviewed, I almost always wake easily and with energy — no matter the time of day it’s set for.

Get natural daylight first thing

Our circadian rhythm — otherwise known as our internal body clock — is regulated by light. Bright light suppresses melatonin, the sleepy hormone, and stimulates cortisol production, which makes us feel awake.

“If you were to deliberately go outside in the morning, soon after waking, you’d get a lot more natural daylight exposure,” Dr. Browning says.

She explains this helps to tell your brain it’s daytime and that we should be awake, and it "helps you feel more alert and helps you suppress melatonin.”

Keep a consistent sleep schedule

When your body clock is regulated, you should wake up feeling refreshed. And a key way to keep it regulated is to go to sleep and wake at the same time every day.

Try to aim to fall asleep within the same hour every night and wake up at the same time every morning. A calming evening routine can make this easier to do.

Repeating the same tasks each night can help build associations that it’s time to wind down and switch off, making it easier to fall asleep, too.

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