When people inquire about working with me, they often say that their dog is fine for xxx amount of time. The reason they give is that their dog is not barking.
Usually, the person is not monitoring their dog on a camera so I always recommend getting cameras set up.
Most often, their dog’s fear is in fact triggered much much earlier than they imagine. 😫 (Which is why I am a fan of getting a professional assessment done To find out about options, I invite you to book a complimentary call with me here).
A trainer colleague of mine told me once about a dog who had been coming to her dog school for many years. He had been there as a puppy and then continued with various courses and activities.

(I came across this picture of a sadly stressed dog. Note the long tongue curled up a bit like a spoon at the end, the stress signal known as ‘spatulate tongue’.)
One day, years later, the family set up a camera for some reason unrelated to the dog. To their horror and amazement, he was pacing round the sitting room, up the stairs, round the landing, down the stairs and round the sitting room for all the hours they were at work.
When they came home, he greeted them perfectly normally as though nothing had happened. They therefore had no idea he had developed a compulsive behaviour to cope with their absences.
During all their working hours he was pacing without once lying down, drinking some water or resting in any way.
This is such a sad story but a perfect example of why we should always monitor our dogs when they are at home alone. They may not be barking but, if they suffer from the fear of being alone at home, they’ll be showing any number of severe stress signals. They will be showing any number of behaviours to try and find relief from the fear.