Why Can't I Sleep? There are only two reasons

Updated: Jan 11, 2021

This article is the first of the five-part Sleep Basics series. To access the Sleep Basics workbook that accompanies these articles, please click here.

The payoffs of getting sleep on track can be enormous—even life-changing—and, with the right knowledge and approach, you can see improvements very quickly.

Unfortunately, there are many traps that can keep you from sleeping well. Because some causes of sleeplessness are sneaky, it's ofter hard to know what you're up against. Luckily, we boil down the many causes to just two main reasons you can't sleep.

The Two Reasons Why You Can't Sleep

At any given time, there are only two potential reasons why you can't sleep.

1. You don't have enough sleep potential

2. You are too activated

If you try to sleep but you don't have enough sleep potential, it's like trying to paint without enough paint. It is just not possible to sleep yet. Attempting sleep when there there is not enough sleep potential creates an opportunity to toss and turn in bed.

There are many things that cause too much activation for a good night's sleep. Some causes are well-known--stress, technology, and caffeine are well-known culprits--whereas some are less obvious. We'll use the DECODE checklist to help you remember the six main causes of high activation.

Sleep Potential

The amount of sleep potential you have at any given time is impacted by the sleep drive system and your body clock system.

Sleep Drive

Sleep drive builds when you are awake and is depleted when you are asleep. An increase in physical activity increases sleep drive.

Imagine you woke up at 6am and went hiking the entire day. If you tried to sleep at 11 pm, you would likely fall asleep easily and have a deep, restorative sleep due to high sleep drive.

In contrast, imagine you slept until noon and spent most of the day inactive. If you attempted to sleep at 11pm, you would likely not want to sleep, struggle to fall sleep, or have a light, broken sleep due to low sleep drive.

A helpful guideline is that you need at least 14 hours awake to build up enough sleep drive.

This explains why a noon wake-up would result in sleeplessness at 11pm. Using the 14-hour guideline, adequate sleep drive would be expected no earlier than 2am.

Napping is another common reason for inadequate sleep drive when attempting sleep. Like a late afternoon snack ruining your appetite for supper, naps help in the moment but deplete sleep drive, resulting in lower potential for overnight sleep.

To summarize, for enough sleep drive, you need to have had enough time awake and enough physical activity.

The Body Clock

The body clock (or circadian rhythm system) has a profound influence on sleep and alertness at different points of its ~24-hour cycle.

Sleeplessness can result when sleep is attempted at a point of alertness during the clock's cycle. If trying to sleep when the clock doesn't think it's time to sleep, the potential for sleep is low.

When clock is delayed, either because of an underlying tendency or, more commonly, because of behaviours that cause the clock to shift later, it is common to not have enough sleep potential in time to get a good night's sleep.

Putting sleep drive and the body clock together

You need BOTH enough sleep drive and circadian signals for sleep to have enough sleep potential.

For example, you may have been awake for long enough and you may have been very physically active (i.e. you have enough sleep drive) but, if you are in the forbidden zone, you will likely experience sleeplessness.

Or, if you are within your ideal sleep window but took a nap, you also may not have enough sleep potential due to low sleep drive.

The amount of sleep potential required varies between individuals and also depends on the level of activation.

If you are calm and relaxed, a moderate amount of sleep potential is likely enough.

If you are very anxious and stressed, you will need much higher potential to override the high level of activation (and on some nights, you may not get there).

High Activation and the DECODE Checklist

If you have enough sleep potential but cannot sleep, you are too activated.

To remember the various factors that can drive high activation, we are going to use the DECODE checklist.

DECODE stands for the following:


E: Environment

C: Cues

O: Overactive mind (i.e. Thoughts)

D: Doings (i.e. Activities and behaviours)

E: Emotions

Let's now go into a bit more detail on each factor.

Drugs, Medications, Food & Drink

Many substances, medications, and foods can contribute to high activation, resulting in difficulty falling asleep and/or poor sleep quality.


An activating environment is a common reason for high activation and sleeplessness.

Casinos exploit the fact that bright lights, cold temperatures, and a busy, stimulating environment keeps us alert late into the night.

Optimizing the environment is often the easiest place to start and, once addressed, requires no further effort or willpower on your part.


We can learn to associate certain triggers or cues with an automatic response.

For example, imagine experienced food poisoning after eating lasagna. After this incident, you feel nauseated and light-headed whenever you smell, see, or think about lasagna. Lasagna is now a cue that brings on a state of nausea.

Similarly, the bed can become a trigger or cue for a state of high activation. This occurs when there has been a lot of time spent awake and alert in bed. This cued response is one of the most common and powerful factors driving chronic issues with sleeplessness.

‘Good sleepers’ have the opposite cued response. They associate the bed with sleepiness and a state of low activation. They can be fully alert at bedtime, then quickly become sleepy upon getting into bed.

One of the most effective interventions for chronic insomnia is the use of strategies called stimulus control strategies to retrain the mind and body to associate the bed with sleepiness and a state of low activation.

Overactive Mind

What we think and how we think can contribute to high activation.

An overactive mind when attempting to sleep is one of the most common causes of sleeplessness.

The mind may be active with worries, thoughts of the past, things that need to get done, plans for the future, or creative ideas.

Sometimes, when sleep has been a problem for a while, unhelpful thoughts about sleep and the consequences of poor sleep drive high anxiety at bedtime, resulting in even more sleeplessness.

Doings (i.e. Activities)

For most people, it takes time (and sometimes effort) to transition from a state of higher activation to a lower state of activation (i.e. deactivate or wind-down).

We need to be in a state of high activation during the day to function optimally. We are so used to being 'on' and there are so many things conspiring to keep us in this state. Unless you explicitly carve out time to deactivate, it is very difficult to get to the state of calm, relaxation needed for good sleep.

There are a number of common offenders that keep us too activated for sleep--exercise, social media, disturbing news, YouTube, Netflix, heated discussion/arguments, to name a few.


Both positive and negative emotions (excitement, anxiety, frustration, sadness) can be associated with a state of high activation. While this may seem obvious, in the moment, it's not uncommon to not be aware of how we're feeling.

When experiencing sleeplessness, it's helpful to take a moment to check-in with your emotions. This may provide some insight into why you cannot sleep or may guide you towards an effective course of action.


Even if you have enough sleep potential, if you are too activated, you will experience sleeplessness (difficulty falling asleep, difficulty staying asleep, or difficulty becoming sleepy).

The DECODE framework provides a helpful checklist to recall the less obvious factors contributing to sleeplessness.

Now that you understand what contributes to inadequate sleep potential and high activation, the next article covers an approach to what to do when you cannot sleep.

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