Dogs go through sleep cycles. Image Credit: docksnflipflops/iStock/GettyImages

Pet parents are usually the first to admit that the canine members of the family act a lot like the human ones. "Talking" during sleep is one common characteristic dogs share with humans. If you hear your dog crying or making other noises in his sleep, you've likely caught him dreaming about something that happened earlier that day or about things dogs typically do.

There's a saying that goes, "Let sleeping dogs lie." Chaucer was the first to use this phrase, all the way back in the year 1380. Even then, people realized that a dog could be unpredictable when they are suddenly disturbed or awakened. A dog that is deep in slumber enough to be crying or whimpering in her sleep is very deeply asleep. Interrupting your dog when she is sleeping this deeply could startle her so much that she might unintentionally bite you.

Dog sleep cycles

Dogs need a lot of sleep. It's not unusual for a dog to spend half the day sleeping . . . literally 12 to 14 hours a day. Puppies and older dogs will sleep even more than this. The phases of dog sleep cycles are very similar to the sleep cycles humans experience, and that includes the rapid eye movement cycle, or REM sleep, when dreaming occurs.

Dogs experience two phases of sleep in a complete cycle: the slow-wave phase and the REM phase. The slow-wave cycle begins as soon as your dog falls asleep and lasts for 10 to 20 minutes. This is followed by the REM cycle. If your dog cries or whimpers while sleeping, it is likely during the REM cycle, when your dog is most deeply asleep.

The length of this complete REM cycle can last 30 to 45 minutes and depends on the dog's size and how old he is. Larger dogs typically dream for approximately five minutes every 45 minutes while smaller dogs only dream for a minute or less every 10 minutes. During peak brain activity during the dream cycle, your dog may cry, whimper, or growl in his sleep.

Do dogs dream?

If you notice that your dog cries while sleeping, don't worry too much that it's a nightmare you need to rescue your dog from. While we can't know for sure what dogs dream about, it's likely that they dream about doggy things and not necessarily the scary dreams that humans have. That said, according to the AKC, it's best to "let sleeping dogs lie" in this case.

All animals need uninterrupted sleep for healthy mental activity, and if your dog is having a scary dream, waking them could result in an unintended bite, or at the least, stress that your dog doesn't need. The AKC suggests gently calling your dog's name, until she wakes up on her own. If she wants to go back to sleep, give her a few pets to soothe her.

Signs your dog is dreaming

During the REM phase, you might notice your dog whimper, cry, or make other noises. You might see their eyes moving behind their eyelids or their whiskers twitching. Other common signs your dog is dreaming is irregular breathing or their legs trembling and moving. Sometimes, a few of these things will happen at the same time.

Seizures in dogs

A dog having a seizure is different than a dreaming dog. According to the AKC, movements during dreams may look uncontrolled, but a seizure may appear even more uncontrolled. A grand mal seizure appears as thrashing or tremors over a dog's entire body. Petit mal seizures may affect just a portion of the body.

Most dogs have a seizure while awake or shortly after waking up but this can happen while a dog is asleep. Normal movement during dreaming may be twitching, kicking, or paddling their legs. These movements typically only last about 30 seconds or less. Movements of a dog having a seizure will be more severe and last longer.

REM behavior disorder

A rare disorder called REM Sleep Behavior Disorder could be responsible for you asking yourself, "Why does my dog cry while sleeping?" This disorder causes a dog to think of its dreams as reality. So when your dog dreams of chasing a rabbit. or squirrel and starts to move her legs, her body typically is in a sleep state so the muscles don't react as if she is actually running.