Fever Dreams: Why do They Happen and Why are They so Weird?

Sickness can cause many physical effects, including chills, sweating, headaches, fatigue, and more (Ames et al.). These are all symptoms of the body’s immune system fighting an infection (Mayo Clinic 2025). The physical symptoms of fever are well researched and documented; however, a much stranger and less studied symptom is fever dreams. They are often characterized by intense emotions, unnatural scales, and a feeling that something is very wrong when nothing obviously frightening is happening (Shredl & Erlacher 2020). This raises a scientific question: why does being sick make dreams feel much stranger than usual?

During a fever, the body is not just “getting too hot.” During infection, immune signals alter the body’s temperature and send signals; one of these signalling molecules is a cytokine (Opp 2005). Cytokines can also influence sleep and other behaviour during illness. This signalling molecule may help explain why sickness also causes fatigue and disrupts normal sleep patterns (Krueger & Maide 1994).

Infection itself can alter sleep. Research suggests that infectious illness can initially increase non-rapid eye movement sleep while suppressing rapid eye movement, or REM, sleep; this raises questions since REM sleep is associated with vivid dreaming (Cerri et al. 2017). However, dreaming can occur outside REM sleep, and illness can fragment sleep, potentially creating more opportunities to remember dreams upon waking (Krueger & Opp 2016).

Temperature regulation and sleep are closely connected in the brain; some neural networks that control sleep overlap with those that maintain body temperature (Cerri & Amici 2021). Even when sleeping, the brain still receives information from the body. During sleep, sounds or physical sensations can enter dreams; the same goes for feelings of heat, chills, discomfort, or sweating (Bach et al. 2002). These sensory inputs are theorized to influence dream content (Karacan et al. 1968).

This could help explain why temperature-related imagery appears more often in fever dreams. However, it does not fully explain other unusual details reported, including spatial distortions such as moving walls or disproportional body parts, or the overall terrifying and uncanny nature of fever dreams (Schredl & Erlacher 2020).

This is where science becomes less certain. Evidence suggests fever dreams differ from ordinary dreams; fever affects immune signalling, sleep, and thermoregulation (Bach et al. 2002), but researchers have yet to identify why these dreams differ from regular dreams. Studying fever dreams is surprisingly difficult because researchers ideally need to locate people with fevers and monitor their temperature and sleep. Many existing studies rely on people remembering fever dreams afterward, creating a recall bias and making conclusions difficult to draw (Shredl & Erlacher 2020; Karacan et al. 1968).

Fever dreams are, for now, best understood as normal dreaming that occurs in an abnormal physiological state. The dreaming brain still does what it normally does and constructs a world from the fragments of sensation it has. It is known that fevers change both the body and sleep, but it’s still unclear why these symptoms become distorted when we sleep (Shredl & Erlacher 2020).

Bibliography

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Bach, Veronique, Frédéric Telliez, and Jean-Pierre Libert. 2002. “The Interaction Between Sleep and Thermoregulation in Adults and Neonates.” Sleep Medicine Reviews 6 (6): 481–92. https://doi.org/10.1053/smrv.2001.0177.

Cerri, Matteo, Marco Luppi, Domenico Tupone, Giovanni Zamboni, and Roberto Amici. 2017. “REM Sleep and Endothermy: Potential Sites and Mechanism of a Reciprocal Interference.” Frontiers in Physiology (Switzerland) 8 (August): 624. PubMed. https://doi.org/10.3389/fphys.2017.00624.

Cerri, Matteo, and Roberto Amici. 2021. “Thermoregulation and Sleep: Functional Interaction and Central Nervous Control.” Comprehensive Physiology (United States) 11 (2): 1591–604. PubMed. https://doi.org/10.1002/cphy.c140012.

Karacan, I, S. M. Wolff, R. L. Williams, C. J. Hursch, and W. B. Webb. 1968. “The Effects of Fever on Sleep and Dream Patterns.” Psychosomatics (England) 9 (6): 331–39. PubMed. https://doi.org/10.1016/S0033-3182(68)71807-7.

Krueger, J. M., and J. A. Majde. 1994. “Microbial Products and Cytokines in Sleep and Fever Regulation.” Critical Reviews in Immunology (United States) 14 (3–4): 355–79. PubMed. https://doi.org/10.1615/critrevimmunol.v14.i3-4.70.

Krueger, J. M., and M. R. Opp. 2016. “Sleep and Microbes.” International Review of Neurobiology 131: 207–25. https://doi.org/10.1016/bs.irn.2016.07.003.

Mayo Clinic. 2022. “Fever – Symptoms and Causes.” Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759.

Schredl, Michael, and Daniel Erlacher. 2020. “Fever Dreams: An Online Study.” Frontiers in Psychology 11 (January). https://doi.org/10.3389/fpsyg.2020.00053.