So you've been away and had a great holiday. You return to pick the dog up from the kennels and she's so excited to see you that she's almost hysterical. That in itself is understandable since she hasn't seen you for a fortnight.
You notice that she has lost a bit of weight and wonder why. When you return home you find that every time you leave the room the dog whines, barks and whimpers. Her voice is hoarse and she might cough quite a bit. She follows you everywhere and if you go out of the house for any length of time she may do uncharacteristic damage to furniture and doors by scratching and chewing. She could also begin to wee or poo indoors whilst you are out. When you return she is overly fussy and takes a long time to calm down.
All these things are signs of your dog having been suffering from anxiety and stress whilst you were on holiday. You wonder if the cough and hoarseness is due to constant barking and whining and your assumption is probably right. She could have been doing exactly that for the majority of the time you were away. Her weight loss is probably due to not eating and the scratching and chewing is probably because she is trying to get out of the house to follow you. The incontinence is also more than likely due to separation anxiety.
Why does this happen in some dogs? All dogs have their own personality just like children do. Imagine the reaction of a shy child who has never been away from home, if you left it in an alien environment with a lot of strange, scary, unruly other children. The child would be terrified; it would not know when or if you were ever going to return. That is probably how the dog feels too.