It turns out that all sleep researchers agree: the single number that best predicts how you feel and performs any given day is your sleep debt. It's not more REM or deep sleep — it's not the stage of sleep you're in when you wake up. If you want to feel better, perform better, pay down your sleep debt, and follow your circadian rhythm. Sleep debt is the sleep you owe your body, based on your personal sleep need, over several days or weeks.
Sleep debt is the result of partial sleep deprivation over several days or weeks. RISE uses the last 14 days of sleep data to calculate your sleep debt in hours. This single number of hours is highly effective at predicting your energy during the day. How you feel right now isn’t just a result of last night’s sleep, it’s the result of the previous two weeks of sleep.
One night won’t mess you up, but it also won’t fix everything. Real benefits will come from managing sleep debt over time with a consistent schedule to meet your sleep need.
Despite what you may have heard, you can make up sleep and pay down sleep debt. It's not forever, but within 14 days, you can accumulate debt and pay it down. A 2018 study published in the Journal of Sleep Research observed that people who paid down sleep debt by sleeping more on the weekends had the same mortality risk as those who slept 7 hours every night.
While a consistent sleep schedule has many benefits, we also know that life happens. What's important to remember is that you can always pay down your sleep debt.
The lower your debt, the more energy you have to be your best.
A 2003 study found mental performance dramatically declined in people who were sleep-deprived yet reported not feeling sleepy. So why do some people still believe they can deprioritize sleep? Caffeine may be one reason since we can use it to counteract low levels of wakefulness. But this use ultimately boomerangs, as caffeine negatively impacts that night's sleep, triggering a vicious cycle.
The more insidious reason some people don’t focus more on sleep debt is humans tend to underestimate just how underslept we are and how impaired our performance is. Indeed, sleep researchers have wondered, if sleep is so crucial to our daily performance, then why don’t we realize it? What they’ve found consistently is significantly sleep-deprived individuals repeatedly rate themselves subjectively as only moderately sleepy. In "The Secret Career Booster That Costs You Nothing" the author aptly describes the findings of seminal research: “Lack of sleep ... apparently tricks you into thinking you’re an office all-star. People who slept just six hours per night for two weeks functioned as poorly as if they’d gone without sleep for 48 hours—yet they thought they were performing at the top of their game.”
The widely adopted framework scientists use for researching fatigue and performance is called the two-process model of sleep regulation — the interaction between sleep debt and circadian rhythm. We call this model the 2 Laws of Sleep and it's the scientific basis of RISE.