Have you ever gone to bed super early, expecting to wake up feeling bright-eyed and refreshed, only to feel tired the next morning?
Well, it turns out there's a very simple explanation for this.
A TikTok user named Addison Jarman has been sharing hacks on her social media pages - including one to find out exactly how much sleep you need.
In a video that's been viewed over five million times, Addison explains why it is that you're often still tired first thing when you wake up, no matter how much of a good night's sleep you had.
Posting under the username @addison.jarman, she said: "Oh my gosh, I'm always so tired when I have to wake up.
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"Why? You go to bed pretty early... I know it makes no sense.
"Actually it does.
"You may not be going to bed at the right time for when you have to wake up.
"We sleep in 90-minute cycles, so I'll wake up feeling way less tired if I wake up at the end of one of these 90-minute cycles."
Addison then shared how to work out the perfect time for you to go to bed at night.
She explained that you start by working out what time you need to be up, then you count backwards in 90-minute blocks.
Addison added in the comments: "Sleep cycles across the night are only approximately 90 minutes in length.
"This cycle is made up of stages that include dozing off, light sleep, deep sleep and REM."
Thousands of people were impressed by the sleep tip, however many said they'd struggle to work it out for themselves as they were "bad at math".
One replied: "Can you please post a schedule? I'm bad at math."
Someone else said: "Is there an app for this? I'm not trying to do math right now..."
A different user added: "That's definitely true, I just can't figure out the right time."
Others vowed to try it out for themselves to see how well it worked.
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