Hello, my name is Dr. Roger Welton, and I am happy to help.
Underlying anxieties in dogs tend to worsen with age. It is likely that Harry had some level of separation anxiety all of this life, as both Springers and Labradors are prone to this type of behavioral issue. Whereas before he may have exhibited signs like a bit of panting or whimpering that went unnoticed, now that he is older and anxiety is potentially manifested more significantly, Harry may be seeking these sheltered areas for reassurance when you are not at home.
In order to aid with relieving separation anxiety, I advise the following tips:
1.) Do not make a big deal about leaving. In fact, ignore Harry for the past 30 minutes before you are leaving the home. Do not even say goodbye. This may seem mean or cold, but it actually helps. When you varying your "leaving the home" routine, you help to prevent Harry from beginning to build up the expectation of you leaving. This could make your absence less impactful.
2.) Likewise, when you return from home, refrain from giving him any sort of greeting or acknowledging that he is there, no matter how much he fusses and yearns to be greeted. Again, while this may seem cold or even mean, providing him that extra gratification of an instant greeting the moment you get home, actually feeds into the separation anxiety, as you make a big deal about your return. Giving him ample time to calm down before greeting him, in Harry's mind, your absence and presence may not cause as much difference in his mind.
Try these simple techniques for a few weeks and see if it makes a difference. If the hiding continues beyond this, you make want to consider some calming herbs like ginger root, Kava, and/or valarian. Some dogs with separation anxiety also respond to treatment with St John's Wort, an herb that raises serotonin in the brain, the neurotransmitter that is responsible for feelings of contentment in the brain and calms feeling of fear and anxiety.
I see that you have been offline, so I will be exiting this chat. If you have any follow up questions or concerns, please feel free to post in the Q&A section following this consultation.