This can be the cause of many other behaviors from aggression to problems in house breaking. Sadly the dog is not the only one that can suffer from it. Pet owners sometimes suffer from separation anxiety from the dog. The article attached to the title explains separation anxiety very well.
The attached article addresses systematic desensitization as the primary approach to relieving separation anxiety. This approach is the only one that will really work. It is time consuming and can be very frustrating. During the initial stages it is best to work with a professional to help you not make mistakes.Many of the published approaches leave out very important information about the process.
Systematic desensitization involves extinction training, and schedules of reinforcement. They do not explain that in the extinction process there are some areas that need to be understood. Extinction training can cause extinction burst. Extinction burst is when the animal's frustration is exhibited in increasing intensity as it gives a final attempt to be successful. If one makes a mistake in this process the dog's intensity to fight the process will be elevated.
Sometimes attached with an extinction burst is extinction aggression. This aggression can be directed anything to include the owner. Should aggression develop it can generalize to other situations. What is often overlook is aggression can produce positive reinforcement for the behavior. When a dog shows aggression humans normally back away. The backing away tells the dog it has won, and as a result positive reinforcement was applied.
Behaviors are never forgotten. They can stop occuring after undergoing extinction training, but can reoccur at any time. This is known as spontaneous recovery. When they do reoccur it is less difficult to extinguish the unwanted behavior than originally.