Dogs left alone for prolonged periods of time may exhibit separation anxiety and self-harm, according to a new documentary on the subject.

During the shooting of Home Alone Dogs, a British documentary investigating the effects of solitude on pet dogs, the crew was struck by the intense, visceral reactions displayed by canines after their owners left for work. The psychological trauma appeared to be more pronounced in dogs whose owners worked longer hours. The most depressed dogs were those with owners returning to work after an extended leave.

“For some dogs the consequences can be shocking, including pacing and spinning on the spot,” a spokesman for the project told The Daily Mail. “Others were seen barking and howling for long periods, defecating and even self-harming.” But what causes this intense reaction?

Researchers note that anxiety and depression may be a consequence of the strong bond developed between a dog and his or her owner. While it’s easy for humans to put this friendship “on hold” for a few hours during workdays, their four-footed pals may have a hard time grasping that such separations are temporary. Believing their owners to be gone forever, some dogs literally go crazy with grief.

“Dogs have a very powerful link to humans. You can train a dog to do all sorts of things and understand our gestures,” explains Dr. John Bradshaw, author of the book In Defence of Dogs. “We expect to turn all that off by saying [to our dogs], ‘We’re going out – relax, have a kip, chew a bone, we’ll be back soon.’ They don’t understand that.”

For this reason, some dogs believe they’re being abandoned or excluded from the family whenever they’re left home alone. The result is a separation anxiety that can last all day. Even when the animal appears to be calm and collected, their stress levels may be through the roof.

“There are dogs who are quiet, but when you look at their physiological stress they are affected as well,” said Dr. Nicola Rooney of the University of Bristol’s veterinary school. However, she noted that the issue could be resolved. Owners can use a variety of strategies to suppress their dogs’ depressive tendencies.

“We don’t want owners to say, ‘My dogs is suffering but I’m working long hours and can’t do anything about it,’ so that lots of dogs get dumped in re-homing centers,” she continued.

So, aside from quitting their jobs or bringing their dog to the office, how can owners ensure the mental well-being of their pets? One option is to gradually build up the amount of time you spend away from your dog. That way, your pet will gradually understand that your leaving the house means that you will return soon, and not that you are gone forever.