Separation anxiety describes genuine distress a dog experiences when left alone, or separated from a particular person. It's more than simply disliking being alone. A dog with separation anxiety often shows signs of real panic, not boredom or naughtiness, and the behaviour typically starts within minutes of being left.
Common signs include persistent barking or howling, destructive behaviour concentrated around doors or windows, toileting indoors despite being fully house trained, and pacing or drooling excessively.