Drooling can be seen in dogs for various reasons. Sometimes it can be behavioral in response to fear. More commonly we can see it from an upset gastrointestinal tract and associated nausea and/or vomiting. Some dogs will drool when they are motion sick after a car ride. Less commonly, dogs will drool in response to pain. Pain can sometimes be hard to localize, but in larger dogs like golden retrievers, I would be most worried about their hips. Another common cause for drooling can be any sort of dental disease. Mouth or associated tooth pain can make a dog very uncomfortable.
Since Sammy is acting abnormally, if it persists, I would definitely have him examined to see if the potential cause can be identified. I hope this information is helpful, and please let me know if you have any further questions.
Yes, drooling could be a sign of anxiety, but it is usually more acute (i.e. the dog that comes into the veterinary clinic for an exam that is nervous). I wouldn't expect to see it as a more chronic and long-lasting symptom.
His symptoms don't seem to fit with an anxious behavior. Keep a close eye in him, and if it continues, have someone examine him.