A pedantic discussion of fatigue and sleepiness

People tend to use the terms feeling ‘tired’ and ‘sleepy’ interchangeably in daily life. However, in sleep science we like to make a distinction between being tired/fatigued and sleepiness.

It sounds a little pedantic, but the reason is because there are important distinctions between these two states. Moreover, the ways to we get more energy when we are fatigued is different than the strategies to feel more alert when we are sleepy.

Therefore, it can be useful to notice these differences to help determine what are the best evidence-based strategies to improve how we are currently feeling.  

In this post, I’ll explain the difference between feeling tired and feeling sleepy, in addition to providing some strategies to be more energized and alert throughout the day.

The difference between being tired and being sleepy

Being tired or fatigued can be a result of physical or mental exhaustion. For example, if you just ran a half-marathon, you’d be pretty physically tired. On the other hand, if you just came out of your 3-hour LSAT exam, you’d be mentally exhausted.

In this case, your body and mind might be very foggy, you have very little energy to engage in further activities, and you’d probably want to rest on your couch or bed. Fatigue pulls for rest after all.

However, you probably wouldn’t be able to fall asleep. The interesting thing about fatigue is that if you are tired, it doesn’t necessarily mean you are sleepy. In fact, chronic insomnia is really a disorder of fatigue. People with insomnia are very tired throughout their day, but it feels like they can’t sleep at all.

This is because the mechanisms that drive fatigue and those that drive sleepiness is very different. Sleepiness is our propensity to fall asleep at any given moment. For example, if you’re reading this post and your eyes are rolling to the back of your head, your head is bobbing up and down, and if you closed your eyes and you could fall asleep within seconds – you’re probably sleepy.

Sloth being a sloth
A case of being tired and sleepy

How being tired tricks us into maintaining insomnia

As we noted before, fatigue can be tricky because it pulls for rest. However, excessive time spent resting can affect our ability to build up the sleep drive we need for high-quality, restorative sleep.

This can lead to a vicious cycle of going to bed feeling exhausted but being unable to fall asleep, trying to sleep-in and rest more the next day, which leads to subsequent poor nights. The result is a case of chronic sleep problems and feelings of exhaustion.

Evidence-based strategies to improve fatigue

People tend to blame their feelings of being tired on not getting sufficient sleep. Although it is possible that improving our sleep can improve our energy levels, there are ultimately many different factors associated with fatigue.

First, it’s important to think of fatigue as more of a generator than a battery. Sometimes we must give a little to get a little. Have there ever been times where you may have decided to go on a walk even though you were feeling tired? How did you feel afterwards? Probably a little better.

That’s the generator at work! This is why some people feel tired despite spending a lot of their day resting.

Beyond activity, there are a number of other factors that you can experiment to see if it helps improve your energy levels: proper diet, hydration, sufficient sunlight, planned activities to reduce boredom, caffeine rebound, and many more. Here’s an article on specific fatigue management strategies to increase your energy!

gentleman jogging
Being active to feel more active

Sleep extension to reduce sleepiness

There are a few ways to know whether sleepiness is a concern for you from a behavioural sleep perspective.

First, you’re spending most of your time in bed asleep. General principles of cognitive behavioural therapy suggests that if you are spending around ~90% of your time sleeping when you are in bed, then you are excessively sleepy.

A second indicator is if you fall asleep within 10 minutes or less on average. The third indicator is evening dozing. For example, falling asleep when you are watching a show with your partner in the evening.

In these cases, sleep therapist will provide a sleep extension. Slowly extend the amount of time by 15-minute increments in bed (either in the morning or at the end of the night) to see if the new window feels better for you throughout the day. For example, if you are spending most of your time in bed sleeping on a 11:00pm to 6:00am schedule, then you could potentially at an extra 15 minutes to the tail end (11:00pm to 6:15am schedule).

If you notice continued dozing throughout your day and feeling sleepy throughout the day, then that can be a sign of sleep apnea, especially when paired with snoring. In this case, it is helpful to check in with a sleep specialist and get a sleep study done.

a cat sleeping on a couch
My reaction when I know I have an extra 15 minutes of sleep


  • Being sleepy and being tired are used interchangeably but are two very distinct states
  • People with insomnia are tired, not sleepy
  • Fatigue is multi-faceted and requires experimentation to test which areas we can improve to increase our energy
  • There are a few different ways to know if sleepiness is a concern and sleep extension is an evidence-based strategy to tackle sleepiness in a gradual way

I hope this post was helpful to understanding the difference between fatigue and sleepiness a little more!

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Best wishes,