Unlike humans, horses sleep more frequently, but for much shorter periods of time. Foals nap about half of each day until they are 3 months old. They sleep lying down but as they get older, they choose to stand. Adult horses sleep about 3 hours daily and are more comfortable standing. Weather can have an impact on comfort as well. They don't like to lie down on cold, wet ground. Because of their weight, lying down puts more pressure on their organs. Horses, as prey animals, feel safer standing up in case they have to make a run for it. However, when in a barn or an area where they feel secure, they might decide to lie down for a quick nap.