One of the characteristics of horses sleep is that they need very little deep REM sleep, which is very different from humans.
A horse can sleep either standing up or lying down, but it can only enter REM sleep when lying down. This is because, as we have said, this phase is characterized by muscle relaxation from the neck down, so if a horse were to enter REM sleep standing up, it would fall over.
Why do they sleep standing up? The reason they sleep standing up has to do with their physiology. Horses are very large animals and lying on one side to rest can put pressure on, constrict, certain blood vessels for long enough to create harmful pressures on some of their vital organs.
Another curiosity about horses is that changes in routine or stress can interrupt the natural course of their sleep phases, which will have short- and long-term consequences.
Finally, to enrich a horse’s resting area you can place toys, such as a ball. And of course, an environment with the right temperature and deprived of acoustic and visual stress is essential for the optimal rest of the horse.