Fever Dreams: What are they and why do they happen?

Ever wondered why your dreams may be more vivid or unpleasant when you have a fever? Don’t worry, you’re not alone. This is something known as a “fever dream”. 

A fever is an elevation in body temperature that is the body’s response to infection or illness. It’s considered a fever when the rise in temperature goes above 37.5 degree celsius and that this rise exceeds normal daily variations. 

Fever is mostly associated with symptoms such as feeling weak, feeling hot/cold, sweating and chills. In addition to these symptoms the fever can induce some various forms of sleep disturbance, in particular something known as “fever dreams”.

What are fever dreams?

Fever dreams are vivid and often unpleasant dreams that have bizarre or frightening content that can involve distortions such as moving walls, various threats and creatures/animals with oversized arms and legs similar to the content of an hallucination. 

They are called ‘fever dreams’ as they are the dreams that occur when someone has a fever. Whilst, the process of dreaming occurs in the same way as all dreams, that is most dreams occur during Rapid Eye Movement (REM) sleep, it’s simply that the content is more unusual and more negative in tone and themes.

What happens during a fever dream?

Nothing unusual occurs during a fever dream necessarily, it is simply a phenomenon where the dream content can be more vivid and more bizarre during a period of illness that includes a fever.  Because most of the dreaming occurs during REM sleep, the muscles are switched off so the person will not thrash about and will not act out their dreams. 

It is important to remember that not everyone experiencing a fever will have bizarre or distressing dreams, and that not everyone will have sleep disturbance, and that they are not harmful. If sleep is markedly disturbed then a negative consequence could be feeling tired and unrefreshed by the sleep.

What may cause a fever dream?

The exact cause of a fever dream is unknown but it is thought to be related to the effects that the rise in body temperature have on the brain. 

The increased heat in the entire body can affect cognitive processing and therefore this appears to make the fever dreams more strange than typical dreams. A similar thing can happen when drugs and alcohol are in the body.

Are fever dreams a bad thing?

No, fever dreams on their own are not necessarily bad for you. However, because the content of the dreams might be unpleasant, frightening and unsettling this may disturb sleep and leave the person who is experiencing fever dreams to feel tired and/or distressed.  

They usually pass once the fever settles so it’s generally a very short term issue, and sometimes sleep is not disturbed. The person may not be disturbed during sleep but might remember the content during the next day.

How might fever dreams differ from normal dreams?

There is not really a definition of a ‘normal’ dream but dreams that occur outside of the context of a fever have less intensity, less bizarre or unusual content and are less likely to have strong themes. Fever dreams only differ from other dreams in terms of the content being more bizarre and more vivid. 

While fever dreams are the result of a fever, nightmares differ from fever dreams in that they are more likely to stem from anxiety or trauma.

Other bizarre, frightening or unsettling dreams that don’t occur in the context of a fever could be related to a sleep disorder such as sleep apnea or narcolepsy. If the bizarre dreams are frequent, causing distress and impacting on quality of life and not occurring in the context of a fever then a sleep study under the care of a sleep physician should be arranged.

Can you prevent fever dreams?

There is no definite fool-proof way to prevent fever dreams, however if you reduce the fever, particularly for the sleeping period, this can reduce the likelihood of them occurring.  

You can reduce the fever by:

• Drink plenty of fluids to prevent dehydration.
• Taking medication such as paracetamol (under guidance) that can reduce fever
• Get sufficient sleep. When hot, as well as if sleep deprived, you’re more likely to have strange or disturbing dreams.

Summary

Fever dreams may occur with a rise in body temperature during illness.

Although they tend to disappear once the fever subsides, there may be things you can do to reduce the fever, such as drinking plenty of fluids, taking medication, and ensuring you get sufficient sleep.

If the dreams or fever persist, and you need more guidance, talk to a healthcare professional.

Related reads:

• How to sleep better | 5 tips from a sleep expert
• How to Get More REM Sleep
• What is sleep & why do we need it?

Reviewed by the Healthylife Advisory Board April 2024.