If you have noticed a difference in behaviour then I would seriously consider a vet consultation. Animals cannot verbally of course let you know if anything is wrong..so we must rely on our professionals to find out.
At 11 years old...your dog can be signalling you that something is off. The dog is feeling insecure...or fearful. Could it be do to pain? Could it be due to a shift in sight/sound?
Please see your vet to rule out any medical issues. That would be my first step.