why do horses sleep standing?

In old fashioned horse lived in forests. He would then sit or lie about an animal like the wall Garden ,Tiger to save himself while he slept. To protect himself, he used to sleep and more than four hours a day.

There is a special kind of action in their bodies to avoid falling  asleep while they sleep. The ligaments that link their bones together fix their joints for the time they want. This is why  horses stand  relaxed and fall  asleep without falling.