If you have ever witnessed a horse having a so-called "episodic event," you aren't likely to soon forget it, particularly if the event occurred while the horse was under saddle. Episodic events are defined here as unusual or unexpected, usually brief (spanning seconds to minutes) behavioral events. Between attacks, affected horses and foals appear totally normal.

At the 11th Congress of the World Equine Veterinary Association, held September 24-27, 2009 in Guarujá, Sao Paulo, Brazil, I.G. Joe Mayhew, BVSc, FRCVS, PhD, Dipl ACVIM, ECVN, from Massey University in New Zealand, relayed the current body of knowledge regarding sleep disorders and seizures and epilepsy in both foals and horses.

"Fainting" has been described in Suffolk, Shetland, Fell, Warmblood, and Miniature Horse foals beginning at a few weeks of age. Affected foals show daytime sleepiness and episodes of partial or total cataplexy (i.e., flaccid paralysis and lack of normal limb reflexes). Adult-onset, inherited narcolepsy has not been reported in horses; however, sporadic idiopathic hypersomnia, or sleep attacks, occur in a variety of breeds. This latter condition is characterized by drowsiness, hanging of the head, buckling of knees, and in some animals, sudden and total collapse to the ground, usually with full recovery in seconds.

In both adults and foals, the sleep attacks appear to be lifelong conditions, but can sometimes be treated with the antidepressant drug imipramine administered via injection two to three times daily. According to Mayhew, such treatment is usually not recommended if the patients aren't injuring themselves during their falling episodes