What Is a Fever Dream?

Why are dreams different when we’re sick with a fever? They’re scary, don’t make sense, and can leave your heart racing.

By Sheryl Grassie

Apr 28th, 2022

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Strictly speaking, a fever dream is one that is more emotionally intense and more discombobulating than a normal dream, and it occurs when you have a fever. The National Institute of Health published a 2013 study in which participants were asked to describe their fever dreams. Some common themes emerged. 

Regarding the qualitative aspect of the dreams, people describe them as more bizarre, difficult to understand, and out of left field. Less resembling real life than their non-fever dreams. They are characterized by less social interaction and people often find themselves alone or abandoned in these dreams which can be quite frightening.

Fever dreams are usually negative. They are themed around bad things happening or bad things about to happen. People often feel threatened in these dreams and helpless. Fever dreams can be much more detailed than a normal dream, and often, there is some sort of spatial distortion, meaning things move in strange ways. Think of a funhouse mirror where you are disproportionately large or small. You know how scary faces are stretched for effect in horror movies. 

Finally, fever dreams have a repetitive nature. It can be that the same thing happens over and over in the dream, or that you have the same dream over and over throughout the night. Some people experience a dream from childhood recurring every time they have a fever. In any case, fever dreams can be quite unpleasant. To recap, they are hallmarked by being:

  • Emotionally intense
  • Difficult to understand
  • More detail than a normal dream
  • More bizarre
  • Alone or socially isolated
  • Feeling threatened or helpless
  • Negatively themed
  • Spatially distorted
  • Repetitive

What Causes a Fever Dream?

When you have a fever, your brain temperature is elevated along with the rest of your body. This elevated temperature can cause changes to the way we perceive things. When you are awake with a fever, you know the feeling of your perceptions being more intense with things like noise being louder, and a slight to moderate special distortion. You can feel dizzy and like things are “off.” Researchers surmise that what causes these waking experiences also causes disturbing dreams, where things are similarly louder, more intense, and spatially distorted. 

The International Journal of Dream Research published a study in 2016 that concluded fever has an effect on the cognitive functioning of the brain, which does indeed impact dreams. It is suspected that a fever changes the way the brain processes.

The Connection to REM Sleep

Debate continues around why humans dream. The understanding has changed as our culture has evolved and dreams have been understood over time as many different things. A way to communicate with the Gods, a form of precognition, the subconscious communicating with the conscious, a connection to the collective unconscious, or probably most recently a way the brain codes, sorts, and files away memories and information have all been ways of understanding why we dream

Normal dreaming, that takes place when we are not sick, happens primarily during rapid eye movement (REM) sleep. The other major function of REM sleep is to manage memory and memories. This may account for why we often have elements of real life like people, places, and things show up in our dreams. The brain may be processing information for storage and your conscious mind experiences awareness of this process as a dream. 

So, why then are the dreams different when you have a fever? Researchers don’t fully have the answer to this question, but there are things we do know that may shed light on it. For instance, people under stress have more bad dreams than people not experiencing stress. Stress dreams are characterized similarly to fever dreams: bizarre, scary, hard to understand. With a fever, the body is under stress, and the same or a similar process may be taking place as during any other kind of stress that causes bad dreams. 

Further, Both mental acuity and general cognition are affected by external as well as internal temperature. When we are hot, we don’t think as clearly and don’t compute as well. When people visit or move to a warmer climate, they can have periods of compromised cognition, poor decision making, or lowered IQ, that usually goes away after a short while when they acclimate to the temperature. Spicy food is linked to increased internal body temperature and to nightmares. Whether internal temperature or outside temperature, our brains function differently when we are exposed to heat or overheated like with a fever.

What Fever Dreams Are Not 

  1. A sign that something is wrong: As uncomfortable as fever dreams can be, they are not a sign of something wrong. They are considered benign and nothing to worry about. 
  2. The same as hallucinations or delirium: Fever dreams are not to be confused with other types of mental confusion that may have less benign causes. Fever, however, can produce waking hallucinations.


Fever dreams are a common and normal occurrence when a person is sick and has a fever. They are described as far more intense, negative, and harder to decipher in comparison to normal day-to-day dreams. Researchers believe there is a link with temperature and brain function that may cause these types of dreams. We dream mostly during REM sleep in tandem with sorting and consolidating memories. Fever affects these functions and changes the normal dream state.