In other words, when you leave for work in the morning, your dog is plunged into a state of nervous anxiety which intensifies extremely quickly.

Dogs are social animals. They need plenty of company and social interaction to keep them happy and content. No dog likes to be left alone for long stretches of time, but some dogs do a lot worse than others. These dogs are the ones most prone to separation anxiety.
There are a number of contributing causes to the condition.

1. Some breeds are genetically predisposed towards anxiety and insecurity, which is something you should consider when deciding which breed you are going to go for (particularly if you're going to be absent for long stretches of time). A few of these breeds include Weimaraners, Springer Spaniels, German Shepherds, and Airedales.

2. A significant proportion of dogs from shelters develop separation anxiety. Most of these shelter dogs have undergone significant trauma in their lives. They have been abandoned by their previous owners, and thus they have little trust that their new-found owner (you) is not going to pull the same trick.

3. Dogs that were separated from their mothers and siblings too early have been identified as being especially prone to separation anxiety. Puppies from pet stores are a perfect example of this.

They are usually taken from their mothers well before the earliest possible age (which is 8 weeks), and confined to a small glass box in the pet store for anywhere between a few weeks to two months.

This early weaning, coupled with the lack of exercise and affection while in the pet store, is psychologically traumatic for the dog.

4. Neglect is the number-one cause of separation anxiety for dogs. If you are absent much more than you are present in your dog's life, separation anxiety is pretty much inevitable. Your dog needs your company, affection, and attention in order to be happy and content.

The symptoms of separation anxiety are pretty distinctive: your dog will usually learn to tell when you are about to leave (she will hear keys jingling, will see you putting on your outdoor clothes, etc) and will become anxious.

She may follow you from room to room, whining, trembling, and crying. Some dogs even become aggressive, in an attempt to stop their owners from leaving.

When you have left, the anxious behavior will rapidly worsen and usually will peak within half an hour. She may bark incessantly, scratch and dig at windows and doors (an attempt to escape from confinement and reunite herself with you), chew inappropriate items, even urinate and defecate inside the house.

In extreme cases, she might self-mutilate by licking or chewing her skin until it's raw, or pulling out fur, or will engage in obsessive-compulsive behaviors, like spinning and tail-chasing.

Upon your return, she will be excessively excited, and will leap around you in a frenzy of delight for a protracted period of time (more than the 30 seconds to one minute of a happy, well-balanced dog.)

This extended greeting is a source of some misunderstanding and without realizing that such a greeting actually signifies the presence of a psychological disorder, some owners actually encourage their dog to get more and more worked up upon their return (by fuelling the dogs excitement, encouraging her to leap around, paying her protracted attention, and so on.)

If you are behaving in this way with your dog, please stop. I know it is tempting and very easy to do, and it seems harmless after all, she is so happy to see you, what harm can it do to return her attention and affection in equal measure? But in actuality, you are just validating her belief that your return is the high point of the day.

So she is as happy as Larry when you return but, when it is time for you to leave again, her now exaggerated happiness at your presence is under threat, and she gets even unhappy when you walk out that door.