One of the more common questions asked about horses is why they sleep standing up. To us humans, this does not sound very comfortable! Horses’ back legs lock so that standing for a long time is not strenuous, so it is much more comfortable than it looks.
The reason horses sleep standing up is so that they are protected from predators. Horses do most of their sleeping during the day, when predators are out and about. Since horses have straight backs, they can’t get up quickly. If they are lying down when a predator comes along, they will not be able to react swiftly enough.
Horses are also more comfortable standing up than lying down. Because they are so heavy, lying down puts a lot of pressure on their downward side. This could lead to tissue damage.
Horses don’t always sleep standing up. A horse will take a short nap during the day lying down to rest his legs. Sometimes a group of horses will lay down to rest, with one horse guarding the others. Horses actually get their deepest sleep while lying down. A horse who is insecure in his surroundings or has health problems which prevent him from lying down, will become sleep deprived.