How and why sleep affects your mood

Waking up after a night of disrupted sleep can really take the shine off your day. Tiredness makes everything feel harder than usual – both mentally and physically. Regular sleep deprivation can also affect your health, increasing your risk of heart disease, diabetes, weight gain, and even cancer.

However, for many, the most obvious effect of a bad night’s sleep is on your mood. You can often tell when someone has not had enough sleep just by how they act.

Too little sleep can have a tremendous impact on your mood and could even contribute to mental health problems. In fact, chronic sleep problems can lead to a higher risk of mood disorders, like depression and anxiety. Research suggests that 15-20% of people diagnosed with insomnia will also develop depression (1).

Lack of sleep can affect your mood in the following ways:

1. Slower thought processes

Chronically tired people often find it hard to pay attention and are more easily distracted and confused. If you realize this is happening, but are still unable to mentally perform at the level you want or need to, it can affect your mood, usually leading to frustration and even anger. This is usually aimed inward but can also be directed at other people.

These disrupted thought processes can also lead to making bad decisions that, if you’d had enough sleep, would never have made. This can have a big impact on all aspects of your day-to-day life and could lead to a regretful state of mind.

2. Impaired memory

Forgetfulness can lead to frustration. For example, if you can’t remember where you left your car keys, you could become increasingly annoyed that you are unable to locate them, and that your search is using up valuable time you wanted to spend doing something else.

Tired brains are less able to turn short-term memories into long-term memories. That means simple tasks like remembering the name of someone you were just introduced to can be much more difficult if you aren’t sleeping properly. This can lead to both embarrassment and social anxiety.

3. Increased emotional reactivity

Lack of sleep makes many people short-tempered. Something that normally hardly registers on your emotional radar can send you into a fit of rage when you are tired. This is because being tired decreases your ability to control your mood and is linked to increased amygdala activity, the part of your brain responsible for emotional control. If you find yourself raging out when stuck in traffic or yelling at the TV for no apparent reason, you are probably sleep-deprived.

4. Loss of empathy, sympathy, and difficulty reading other people’s moods and emotions

Too little sleep can affect your ability to read and relate to other people. It affects the parts of your brain responsible for recognizing and understanding visual and verbal cues. Not being able to empathize with the people around you can create a hostile environment. You may be thought of as aloof or uncaring. In reality, you are just less able to read and respond to their face and voice because you are too tired to do so.

5. Increased anxiety and stress

Anxiety, stress, and insomnia are inextricably linked. Being stressed or anxious can stop you from sleeping, and not sleeping means you are less able to cope with anxiety and stress. This creates a vicious circle that can be hard to escape from. Because sleep can affect your day-to-day ability to function, this can make you feel even more stressed and anxious, further disrupting your sleep.

6. Poor self-image

Lack of sleep affects not only how you feel, but how you look too. In turn, this can affect your self-image, self-worth, and your ability to do your job. Ultimately, poor self-image can change your entire outlook on life, possibly leading to thwarted ambition and even depression. 

7. Lack of willpower

Tiredness can drain your willpower, making it harder to do things like eat healthily or exercise regularly. Giving in to the temptation to eat unhealthily or skip your workout can lead to feelings of guilt. Getting enough sleep not only increases your physical energy, but it also helps strengthen your resolve to do those things you might otherwise prefer to avoid. After all, who wouldn’t rather eat takeout pizza instead of cooking a healthy meal?

Lack of sleep can make it harder to stick to your healthy eating and exercise regimen, even though you know you should. Not getting enough exercise and eating unhealthily can affect your mood.

8. Impaired immune system function

While your immune system is very much part of your physical health, it can also affect your mental health, too, albeit indirectly. Long-term insomnia can stop your immune system from working correctly, leading to more frequent and longer-lasting illnesses. Being ill all the time can have a significant impact on many aspects of your mental health.

For example, having to take time off work in a very competitive office can mean job insecurity, giving rise to feelings of anxiety and stress. Needless to say, anxiety and stress are not conducive to a good night’s sleep.


Not getting enough sleep can impact on all aspects of your mood. Some of these effects are direct, while others are less so. It doesn’t take a large sleep deficit to upset your mood. Even one less hour of sleep per night for a week produces measurable changes in mood. The bottom line is that if you want to feel and perform at your best, getting enough sleep is crucial.


1. Harvard Medical School: Sleep and mood

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