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You know when you think you got a decent amount of sleep, at least 8 hours, and yet you still woke up groggy? Why is that? You got plenty of sleep! That's what 15-year-old Minnesotan Josh Ternyak wanted to figure out. He was having the same problem until he created his sleep calculator.

Sleep is a weird thing. 8 hours is the typical amount of sleep that is suggested but you also need to make sure you wake up at the correct timing in your REM cycle or, no matter how much sleep you get, you'll still wake up groggy.

What the heck is your REM cycle? According to Dr. Ranji Varghese, who is a medical director at Hennepin Healthcare's Minnesota Regional Sleep Disorders Center, who spoke with KARE 11, REM cycles are broken up into two parts: REM sleep and non-REM sleep. The key is to wake up during REM sleep.

REM sleep is when you dream most vividly but it's also when you are sleeping the lightest. So because this is a light stage of sleep, you want to wake up during that time. If you don't you wake up during the non-REM sleep stage which is when you are sleeping the deepest. Hence the reason why you would wake up groggy, you probably woke up during non-REM sleep.

How do you figure out when to wake up then? That's where Josh's sleep calculator comes in! All you need to do is plug in when you need to wake up and the sleep calculator will tell you what time you need to go to bed in order to wake up during a REM sleep stage. Pretty cool, right!