If a horses collapses at rest, it is often because there is a problem within the nervous system. If the brain is not sending the right messages, the body can’t respond and will tend to topple over.
Narcolepsy is one such syndrome. This is a rare, incurable sleep disorder of the central nervous system characterised by uncontrolled episodes of loss of muscle tone (cataplexy) and sleep.
The disease has been reported in Shetland and miniature foals (called the fainting disease) and Welsh ponies, as well as the Thoroughbred, Quarter Horse, Morgan, Appaloosa, and Standardbreds.
Narcolepsy is the classic cause of a horse flopping to the floor, as opposed to a fit or seizure. With a fit, the affected animal is likely to be stiff and rigid with involuntary twitches and paddling of the limbs.
With narcolepsy, there is usually a rapid onset of collapse, or sometimes excessive drowsiness and head droop. Horses may buckle at the fetlock and knees and stumble. Sometimes they will sink to the ground, but others will appear to wake up and regain their feet. They may have difficulty moving and are hard to lead because they are unco-ordinated, as if they are sleepwalking.
These episodes can occur rarely or frequently; indeed, with some horses they are seen several times a day. Pony breeds are more likely to become recumbent. Episodes may last from a few seconds to 10min.
Narcolepsy can happen in people and animals as a tendency to fall asleep inappropriately and can happen at any time. Horses can have episodes of narcolepsy following routine daily events, such as grooming, tacking up or even exercise. It is rare for it to happen while a horse is being ridden, but the risk is there and I would not want to ride a known narcoleptic.
The prognosis for narcolepsy varies. Some newborn Thoroughbreds and miniature horse foals may have severe attacks, but can recover fully. Horses which develop the disease as adults are likely to continue having collapsing episodes. There are medical treatment options, but any medication is a double-edged sword that may have damaging side effects as well as possible benefits.
It is something to be carefully discussed with your own vet. Some cases can be managed by a change in routine, such as altering the way they are tacked up, so they are less likely to doze off.
There are some horses with so-called pseudo-narcolepsy. Normally, horses manage to sleep very effectively on their feet due to the amazing anatomical design that locks their limbs. Most healthy horses also lie down at least once a day to obtain proper rest in deep sleep.
If a horse is unwilling or unable to lie down due to various factors, such as inadequate bedding, bullying by other horses or chronic pain that prevents his limbs bending properly, then he will fall asleep standing simply due to fatigue.
In such cases a change in management, such as removing the horse from the other horses, a deep, comfortable bed and painkillers may help.
There are many possible causes of collapse, lots of which will remain undiagnosed despite complex investigations. Remember it can be hard to distinguish the true collapse from the horse who just lies down.