For some dogs these are a threat. They will react with a ‘fight or flight’ impulse - which would help them survive in the wild.
It is connected to the release of adrenalin, enhancing physical strength, heart activity and breathing frequency to ensure that muscles are better supplied with oxygen. This adrenaline boost and the ‘fight or flight’ reaction are triggered by particular stimuli. A dog will perceive these but it will not always be clear to us as humans what is causing the anxiety, and why our dog is trembling, hiding or attacking. Sometimes there is a mistaken triggering, where the dog forms a connection between seemingly unrelated events and the scary situation or pain that has been experienced in the past. Many human companions are familiar with their dog coming into contact with an electric fence around a field and getting a shock. After this, many dogs will form a connection between the livestock on the field and the pain. In future, those animals will be the trigger. Another example is illustrated by a dog I know who reacted aggressively when people around him drank alcohol, even just a sip. The human companion had adopted the dog from an animal shelter, and it turns out that he had been rescued from a previous human companion who was alcoholic and hit the dog when he was drunk.
A fight-or-flight reaction might also be triggered when a dog is left alone in the apartment or house, and feels abandoned. Although he is actually safe and there is no danger to fight or flee from, the fear triggers the adrenaline and this leads to action: shredding sofas, biting doors, chewing shoes or even attacking people who enter the apartment. One person I knew left their dog in the car for a while and when he returned, the padding was hanging out of the seats, the dashboard was scratched and had bite marks, and even the door padding was ripped.
Sometimes one single traumatic experience is enough to leave a deep-seated fear in the dog and cause a trauma. The consequence is that a particular behaviour program will then run automatically whenever a similar situation occurs.
So what is the best way to deal with this? Firstly, it is recommended to acknowledge the effect and try to avoid the problematic situation. Once your dog trusts you and you can convey a feeling of safety by being near them, then you can begin to try and adjust their reactions: try to associate a positive experience or reward with the stimulus that triggered fear or anxiety. This can help the dog to change its accustomed ‘stimulus-threat’ response. If we take the example of feeling abandoned, then you can leave the room and return fairly quickly with a reward for the dog. Then train this with increasing lengths of time before you return. However, where reactions and trauma are too serious, you should seek support from a suitable dog trainer or behavioural therapist.