You may feel alarmed when your dog whimpers during his sleep and may wonder if you should wake him up. As the popular saying goes "let sleeping dogs lie." Dogs can be quite vocal during their sleep often whimpering, crying, barking and even howling out loud. In most cases, there's nothing to worry about; chances are Mr. Sandman just sprinkled a touch of sleepy dust over Scruffy's forehead.
Drifting into dream world
The brains of dogs, just like the brains of humans, undergo similar stages of electrical activity during sleep suggesting your dog also is capable of dreaming. If you watch your dog carefully as he drifts into sleep, you may notice how his breathing at some point becomes shallow and irregular. Soon, you'll notice his eyelids moving quickly as if he was looking at imaginary images. These rapid eye movements occur during the REM phase which is when dreaming takes place. Muscle twitching and vocalizations such as whimpering often also are seen during this time.
Reenacting daily events
Humans may never know what dogs dream about, but some assumptions can be made. Most likely, dogs are reliving the memories of events that occurred earlier during the awake state, theorizes Matthew Wilson, a researcher of the Massachusetts Institute of Technology. So as your dog is twitching and moving his legs, it could be he's dreaming about some rabbits he chased earlier that day, or if he's whimpering, he may be recalling when you left him alone or gave him that dreaded pedicure he really dislikes.
You may feel bad for your dog when his whimpering sounds as if he's having a bad dream. As tempting as it may be to wake him up, don't. Just like you, your dog depends on his beauty sleep to recharge his batteries. A good amount of uninterrupted sleep is essential for his healthy mental activity. Also, consider that if your dog is having a bad dream, waking him up may startle him and potentially lead to a defensive reaction.
Make sure your dog is sleeping when he's whimpering. If not, the whimpering may be his way of trying to grab your attention. For instance, if you are crate training a puppy, the whimpering may be the pup's way of telling you he needs to be taken out to potty. Your dog may be thirsty, or too hot or cold. In some cases, he may be hoping for attention because he feels lonely or bored. Consider that whimpering before sleeping or in the middle of the night may be triggered by some sort of discomfort or pain. Consult with your veterinarian if there is a concern about the whimpering.