February 26, 2026, 4:02 pm | Read time: 5 minutes
In the early morning, the horse is still in the stall, its head hanging unusually low. It appears tired, sways slightly, and briefly buckles at the front legs. Such signs initially seem nonspecific and are not always associated with sleep. PETBOOK explains how dangerous narcolepsy can be for horses, which signs should be taken seriously, and why the cause should be carefully investigated.
What Happens with Sleep Deprivation?
Horses need about five to nine hours of total sleep daily. This is spread over 24 hours and includes dozing while standing and deep sleep while lying down. At night, horses sleep an average of about three to four hours. The so-called REM phase is crucial for regeneration. REM stands for “Rapid Eye Movement.” In this phase, the muscles relax completely, and the brain processes experiences.
This REM phase can only occur in horses while lying down—either in a chest position with the head supported or in a complete side position. While horses can rest standing and enter other sleep phases, full muscle relaxation of the REM phase is not possible while standing.
If this phase is absent for an extended period, a REM sleep deficit occurs. The horse is then not sufficiently regenerated. Sudden sleep moments can occur, where muscle tension abruptly decreases. This can be due to a lack of REM phases or congenital narcolepsy in the horse.1
Causes of Narcolepsy in Horses
Sudden buckling or falling is often referred to as narcolepsy. In adult horses, it is usually not true congenital narcolepsy but rather a so-called REM sleep deficit, also known as “sleep deprivation.”
Narcolepsy in horses is rare, occurs due to breed, and is evident in foals. Affected foals suddenly fall asleep while walking, playing, or drinking and are difficult to wake. Narcolepsy is a neurological disorder.2
However, chronic sleep deprivation due to missing REM phases is much more common. Causes can include:
- Unsuitable living conditions, lack of or damp bedding
- Too small or uncomfortable lying areas
- Pain when lying down or getting up, such as from diseases or inflammations
- Disturbances in the environment, unrest in the stable
- Disrupted social structures in the herd
- Monotony
- Lyme disease
As every horse owner knows, horses are flight animals. This means that the feeling of safety plays a significant role—horses only lie down when they feel safe. If this feeling is absent for a long time, they avoid lying down—and thus the important REM phase.
How Owners Can Recognize Symptoms of Narcolepsy
Symptoms of sleep deprivation or narcolepsy usually appear gradually. For owners, this means: If they feel something is wrong, they should closely observe the horse. It is advisable to take the time to watch the horse over an extended period. It’s best to inform the stable owner as well, so they can also report any abnormalities. Individual episodes may go unnoticed. Typical symptoms include:
- Dozing with a deeply hanging head
- Swaying
- Buckling of the front legs
- Sudden collapse
- Injuries to the carpal joints, fetlock joints, head, or lips
- Abrasions or scars in these areas
- Muscle tremors
- Extreme weakness
- Uncoordinated gait (ataxia)
Some horses rest their heads on the stall door, lean them against the feed trough, or back into a corner. This may be an attempt to stabilize themselves during fatigue.
The collapse occurs because the horse enters a REM phase while standing. It loses muscle tension completely and collapses, posing a high risk of injury.
How Is Sleep Deprivation Diagnosed in Horses?
The diagnosis of narcolepsy in horses is carried out by a veterinarian. Initially, a clinical examination is performed, followed by a neurological examination.3
The following examinations are often conducted:
- Blood tests
- Examination of the cardiovascular system
- Lameness examination
- Assessment for back pain
In many cases, affected horses stay in a clinic for several days. There, their sleep behavior is monitored via video. Additionally, an electrocardiogram (EKG) can be performed to rule out heart rhythm disorders.
Studies with so-called polysomnographic measurements—comparable to examinations in human sleep labs—show that affected horses have significantly less deep and REM sleep. At the same time, there are no indications of central nervous system disorders or abnormal blood values.
Narcolepsy in Horses Is Not Curable
The treatment of sleep deprivation or narcolepsy in horses depends on the cause. For REM sleep deprivation, eliminating the triggering factors is the priority. If living conditions are improved or pain is treated, sleep behavior often normalizes. With sufficient lying sleep, symptoms often disappear quickly.
With true narcolepsy, the situation is different. It is considered incurable, although further research is needed.
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Prognosis
The prognosis largely depends on the cause. For REM sleep deprivation, it is generally good if the triggering factors are identified and addressed. Once the horse can sleep sufficiently while lying down again, daytime sleepiness and collapse episodes usually decrease.
For true, congenital narcolepsy in horses, the course is individually different. The condition is rare and primarily occurs in foals.
Can Sleep Deprivation in Horses Be Prevented?
Since the more common REM sleep deprivation is often due to living conditions, management plays a central role. Important factors include:
- Sufficiently large and dry lying areas
- Suitable bedding
- As quiet as possible night phases in the stable
- Stable social structures
- Assessment and treatment of painful conditions
If owners repeatedly observe dozing with a deeply lowered head, buckling, or unexplained injuries to the front legs, this should be taken seriously and checked by a veterinarian. Chronic sleep deprivation is not a harmless condition but can lead to severe injuries and health consequences.