Dogs who suffer with separation anxiety do not cope well when left on their own. Some immediately go into a state of panic as soon as the door is closed, whilst others may seem to be OK when you leave but on your return the evidence of stress is obvious through the damage they do or a complaint from the neighbours with regard to the barking and howling that occurs during your absence.
The dog being in a stressed state requires the owner to change their association towards being left alone to a more positive state and to show them that there is nothing to fear and to make sure they are in a calm state throughout the absenteeism. This is possible through working slowly and consistently, interacting with the dog is the key and depending on the dog and the effort put in, need not take too long. The result being a calm, well behaved dog and happy to be left alone dog.