WAKING up feeling well rested can feel like a distant dream.

Even if you're getting enough sleep you can feel exhausted for what feels like no reason.

It turns out, there's a really simple reason you spend the entire day yawning despite getting a seemingly peaceful slumber.

Sleep pro Addison Jarman recently shared the simple science behind it all.

We sleep in 90 minute cycles, she says, so if you wake up the in the middle of one of those cycles you're going to find it harder to wake up.

Even if you have a full night's sleep, waking up at the wrong point in the cycle might leave you feeling drowsy.

Our sleep cycle made up of 65 minutes of normal, non-REM sleep, 20 minutes of REM sleep and a final 5 minutes of non-REM sleep.

Which means if you were to wake up without any disturbances or alarms, it's unlikely you'd wake up after eight hours.

Nine hours or seven and a half hours is more likely, since this fits into the 90 minute cycles.

The sleeping pro suggests working out when you should go to sleep by working backwards from when you need to wake up.

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Counting backwards in 90 minute increments will ensure you complete your sleep cycle.

Addison says that it's less about when you wake up and more about when you go to sleep.

So, in theory you could get less sleep, but still feel more rested than if you sleep for longer but wake up mid-cycle.

Viewers couldn't believe how simple the advice was: "Is that why when I get six hours I feel more rested than eight?"

Another joked: "I'd rather wake up exhausted everyday of my life than count backwards in 90 minute blocks just once."

A third quipped: "Wait, people can decide when they go to sleep?!"