Why does my dog sleep with his eyes open?

A dog sleeping with his eyes open is completely normal. This is a trait derived from their wild ancestors. Sleeping with their eyes open allowed dogs to appear awake and to thereby ward off any potential predators while taking a snooze.

Because some dogs may also experience seizures while they are asleep, it's important to know the difference between sleeping with eyes open and having a seizure. A dog that is sleeping with his eyes open will often have a soft look to him. Even though the eyes are open, they are relaxed and peaceful. He may experience slight twitching as he enters the REM sleep cycle, but as a whole he appears content and healthy. A dog that is having a seizure will often have a wide-eyed, empty stare and be jerking in an uncontrollable manner. He may also let out an involuntary cry of pain, lose control of his bowels, or foam at the mouth. If you believe your dog is experiencing a seizure, do not move him. You must let the seizure run its course. Afterwards, seek a veterinarian's attention immediately.

Sometimes dogs dream with their eyes open. Also be aware eyes open during sleep can mean they be having a seizure.