Horses, like humans, also dream. That is known because they reproduce each and every one of the phases of sleep that we recognize in humans.
It has been verified that the dream of the horses goes through four phases, same number as humans.
The first phase is that of wakefulness. The second phase is that of drowsiness that takes up most of the time. Phase three is what is known as slow sleep waves. The fourth phase is REM sleep. In it, the horse can stand up or lie down resting on its sternum and with its legs tucked in. In some cases, the animal has enough room it will stretch as long as it is.
The activity of the brain in horses has a similarity to that which the human being experiences with the dream experience. This phase is known as REM (Rapid Eye Movements) sleep or paradoxical sleep. Therefore, we can intuit that horses very probably dream, although the content of said dreams is impossible to know.
Unlike humans, horses need very little REM sleep time: 2-3 minutes each day. This part of a sleep cycle is recognized as “deep sleep.”
Due to their large size, staying on the ground for a long time could hinder their blood circulation and cause them to increase the internal pressure on their organs, which could be dangerous for their health, for this reason they generally rest standing up.
On the other hand, horses are known to survive on minimal amounts of sleep. They only sleep about three hours a day and never rest for long periods. By sleeping so little time, they generate sleep cycles spread throughout the day in the form of short periods of rest. This means that despite getting an estimated total of three hours of sleep, they need to rest frequently throughout the entire day.
So, maybe the time is short, but when you see them sleeping, maybe they are dreaming of sharing some chukkers with you.