London - A stressful day often leads to a night of tossing and turning even for dogs.
Being separated from their owner for a short time or the presence of a threatening stranger can disrupt their sleeping patterns, researchers found.
A bad day for a dog means less deep sleep, say the Hungarian team, who recorded the brainwaves of 16 animals.
Over three hours of nap time, stressed dogs spent up to 20 fewer minutes in non-REM "deep sleep" than dogs who had just played a game and been made a fuss of by their owners. The study's lead author, Dr Anna Kis from the Academy of Sciences, said: "This would not be a problem for dogs if it happened every so often.
"But over a longer time a lack of good quality sleep could stop them consolidating memories and dealing with their emotions. That could make pets more aggressive or less able to work."
Researchers measured the sleep of dogs including a golden retriever, labrador, sheepdog and Jack Russell over three hours in a laboratory. Prior to sleeping, they were given good or bad experiences.
The lucky dogs spent six minutes with their owners, playing tug of war or "fetch" and being petted and spoken to when they went up to them.
Those in the negative group were left alone on a lead attached to the door and ignored by their owner who did not make eye contact. Then a researcher slowly entered the room in a threatening manner, looking steadily into the eyes of the dog but saying nothing. After a difficult experience, dogs had only 40 to 50 minutes of deep non-REM sleep, compared to an hour for those who were sleeping normally.
Gudrun Ravetz, of the British Veterinary Association, said: "While it is a small study and further studies would be needed to understand the issue in more detail, we know that positive interactions with our pets are important for their health."