Have you ever stayed up late to watch a sports game? Pulled an all-nighter to study for a test? Woken up at 4 AM to catch a flight? Slept late after a crazy party? If your answer to any of these questions was yes, chances are that you have lost out on a full night’s sleep in the process.
All of these excursions are a natural and often regular part of our lives. Nevertheless, the sleep we lose for them is not without its repercussions. Sleep loss is responsible for fatigue, poor cognitive functioning, heart disease, depression, and other chronic diseases.
What if I told you that there was a way to objectively catch-up on the sleep you lost?
Not long ago, I worked for the flight operations department at an airline to design a Fatigue Risk Management System (FRMS). Due to the nature of their job, pilots are required to perform their duties at odd hours, when most of us would be sleeping. The effects of sleep loss are a serious threat to their wellbeing. The FRMS was designed to act as a safeguard against exactly these effects, to maintain flight safety. While brainstorming solutions back when it was still in development, I came across an interesting way of thinking about sleep.
Think of sleep as a currency (let’s call it Sleep Credit). You earn Sleep Credit for every hour you are in bed and you spend some of it every hour that you are awake.
Your goal is to breakeven at the end of every 24 hours to end up with a net balance of 0 Sleep Credits. 8 hours of sleep is the generally recommended amount of sleep for an adult, which leaves us with 16 hours of wakefulness. Therefore, to end up with a zero balance every day, we earn 2 Credits for every hour we sleep (16 Credits for 8 hours of sleep) and we lose 1 Credit for every hour that we are awake (16 Credits spent for 16 hours of wakefulness).
Let’s assume that you normally sleep from 10 PM to 6 AM every day for 8 hours. But today, you plan to stay up till 2 AM to watch a movie with your family. You will be losing 4 hours of sleep, leaving you a debt of 8 Sleep Credits (2 per hour of sleep loss). Knowing this, you can sleep for 4 hours in the afternoon or for 4 extra hours in the morning to make up that debt.
This is an ideal solution for when you lose out on your usual sleep hours to reset your sleep debt within the same 24-hour cycle. However, this may not always be possible due to work or other chores in the afternoon, or because your body wakes you up early in the morning despite you having slept late. Not to worry.
If you’ve had a busy week where you have lost a total of 6 hours of sleep (a debt of 12 Sleep Credits) from Monday to Friday, you can strive to pay off the debt on the weekend. A key thing to remember is that you can never earn more than 16 Credits per day (for 8 hours of sleep) because the quality of sleep beyond 8 hours is not the same as the rest. However, by sleeping more than 8 hours on the weekend, you reduce the hours you spend awake, thereby reducing the number of Credits you ‘spend’. In this case, to make up 6 hours of sleep, you could sleep for 12 hours on Friday, Saturday, and Sunday. In effect, this would reduce 12 of your wakefulness hours, saving you 12 Sleep Credits that can count against the Sleep Debt.
How can you use the sleep credit system to plan your sleep better?
We don’t have an on-off switch for our sleep. It is much easier to sleep at certain times than it is at others. According to this system, the amount of sleep debt we rack up is positively related to the sleep pressure. The higher the debt, the higher the sleep pressure, and the easier it will be to sleep.
Since we are considering 16 hours of wakefulness per day as average, the maximum sleep debt you can accrue through the day is 16 (spending 16 sleep credits). At this point, sleep pressure will be at its highest. Keeping this in mind, consider the following two scenarios:
1. You have to stay up late at night till 2 AM
Assuming that you wake up at 6 AM, by 2 AM you would have spent 20 sleep credits. That is a pretty high level of sleep pressure. To reduce the sleep debt you have at 2 AM to 16, you can sleep for 2 hours in the day to gain 4 sleep credits and offset your wakefulness hours.
2. You have to wake up early in the morning (at 4 AM) but still want your 8 hours of sleep
This scenario requires some more planning. To wake up at 4 AM with 8 hours of sleep, you would have to sleep at 8 PM the previous night. I think most of us would find it difficult to fall asleep naturally at that time, and this makes sense according to the system too. Let’s say you woke up at 7 AM the previous day; you would have racked up a debt of 13 sleep credits by 8 PM, which is lower than the optimum 16 sleep credit debt required for the perfect sleep pressure.
To address this, you have to plan your previous day such that you wake up 16 hours before the time you intend to sleep, to get 8 hours of sleep for the following day. In this example, it would mean waking up at 4 AM the previous day too, building up a sleep debt of 16 sleep credits by 8 PM, and making it is easier to fall asleep.
- Not all sleep is created equal
Generally, the sleep that we get during 3–5 AM is of superior quality than any other time due to our bodies’ circadian rhythms that ebb and flow naturally during a 24-hour cycle. The time between 3 and 5 AM is when they dip to their lowest activity level, allowing us to sleep the best during that time. Losing this sleep may have more serious consequences than at other times.
2. There are different kinds of sleep
There are different types of sleep — REM and non-REM and both serve different purposes. When we get a full night’s sleep, our body goes through a natural sleep cycle which includes the required amount of each type. When we do not get continuous sleep for 8 hours, one of the two may be affected. Therefore, no credit system can compete with a full night’s sleep.
3. Not everyone sleeps the same
We all need different amounts of sleep based on our body, mind, age, etc. The 8-hour average is frequently cited, but needs may differ from person to person.
It is easy enough to modify the system. Just divide the number of hours you usually stay awake by the amount of time you usually sleep. For example, if you sleep for 6 hours every day and stay awake for 18, each hour you sleep is now worth 3 sleep credits (18 credits earned from a full night’s sleep)