When strange people, dogs, or dogs arrive in a new environment, the dog will be wary. It may also be caused by fear, so the tail tends to droop. At the same time, injuries to the lumbar spine can also cause tail droop, and most of them have a history of trauma.
Care Hacks
Why is the dog's tail suddenly hanging down?

A dog's tail is drooping, which means that it is in a bad mood at the moment and is relatively depressed. When a dog feels depressed or lonely, its tail will hang low. Of course, when a pet dog is sick, its tail will also droop.