Dogs who suffer from separation anxiety immediately fall into a state of panic when they are left alone, or when they realize they may be left alone. They are not in control of their actions after that moment just like someone who is afraid of heights is not in control of the terror they feel when in a tall building and need to escape or someone who is fearful of snakes who has just come across a garden snake. We may not understand it, but to that person and DOG the fear and panic is very, very real. Dogs cannot process that you are just running to the mailbox or that you come back every time you leave for work. Logic simply does not apply. Their emotional state has taken over and their system is flooded with cortisol and adrenalin and the amygdala (the emotion center of the brain) is running the show. They are over their stress threshold the moment you pick up the keys, or put on your shoes, or open the door (every case is different).