You've heard it before — everybody should get at least eight hours of sleep a night. But how true is that? After all, surely you've had nights where you've gotten less and felt great and more and felt terrible. 

Well, sleep expert Dr. Michael Breus calls the 8-hour rule a myth. 

"Everybody has a different sleep need in terms of the amount of sleep that they need," the doc explains. "And that's also based on the quality of the sleep that they're getting." 

"If you get really good quality sleep, you don't actually need 8 hours," he continues. "Let's be super clear — 8 hours is a myth. Not everybody needs 8 hours."

(Gasping? Us too.)

In fact, Dr. Breus himself gets 6 to 6.5 hours of sleep each night, he says. 

"I go to bed at midnight and get up around 6:30am," the doctor tells us. "That works for me because of the consistency of my sleep schedule." 

BUT that many hours of sleep wasn't always enough for him. 

The doc used to get 7.5 hours — which is what the average person gets. The average sleep cycle is 90 minutes, he says, and the average person has five of those. (5 x 90 = 450 minutes, or 7.5 hours)

"Because of my consistency," Dr. Breus explains, "I actually started at 7.5 hours and it slowly has shrunk." In other words, he has trained his body to know the best time to go to bed in order to get the most quality sleep. 

So, how do you figure out the best time to go to bed? Well, you'll want to determine what kind of sleeper you are first.

Dr. Breus says there are four different chronotypes — or types of sleepers. 

RELATED: What's Your Chronotype? Take The Sleep Doctor's Quiz

WHAT KIND OF SLEEPER ARE YOU?

Lions
- Morning people
- Most alert first thing in the morning

Bears
- Sleep/wake patterns follow the sun
- Most alert mid-morning

Wolves
- Night people
- Most alert from noon to 2pm and again in the evening

Dolphins
- Light sleepers
- Most alert mid-morning through early afternoon

To learn what chronotype you are and what advice Dr. Breus has for each, take his Chronotype Quiz here.