How do horses sleep? If you ask that question, many will answer that they sleep standing up. But the answer is more complicated than that. Horses nap or doze standing up and require deep REM sleep (rapid eye movement) for 30 minutes a day to be fully rested. This REM sleep is only accomplished while lying down.
One of the greatest myths in the equestrian world is that horses sleep standing up, in part, because it’s true. While horses do doze and nap standing up, because of the stay apparatus, an intricate system of tendons, ligaments, and muscles, they also require rapid eye movement (REM) sleep, which they can only enter while lying down.