I don't know what this is, but it's definitely not that he's guarding you. Does he have something with him at the times that he is behaving this way? Is he on HIS bed? Is there anything that he may be trying to keep you both away from, or is he afraid your going to do something he doesn't like? I don't mean a punishment, but maybe confine him to an area or something? It's very unusual behavior for a typical Golden.
I would start with a trip to the vet for a thorough check up, including a full blood panel. I would also see how he reacts at the vet. I'm just really wondering if it's medical. The way you describe it sounds like he could be maybe having a seizure. I'm no expert but I would definitely start at the vet.
If it is typical resource guarding everything in the posts above should help, but I'm just not sure that's it.
I have an 8 year old male that will actually "guard" me, if you want to call it that. He's absolutely never bitten, or snapped at anyone. People do clearly know that he means business though. He positions himself directly in front of me and gives a very deep bark followed by a snarl. He absolutely only does this when something isn't right. We live on a farm and have a business at our home. He is great with everyone, but occasionally we will have people come up at very inappropriate times. If it's dark out and I am alone walking him and someone comes up the driveway and gets out of their car he immediately drops to his butt directly in front of my feet and clearly warns them to stay put. I am in complete control of the situation however, and learned this very early on. I give him a clear HEAL command followed by SIT and he stays with me no matter what. If it's someone that I like I simply say give me a minute to put him in the house. If it's someone that shouldn't be here they normally ask if he bites and I say yes.
It works like a charm to get them to go away. I have no idea if he would actually ever bite someone, but I think that if I totally overreacted, or was really stressed he may.
That being said my house is a very social place. He's grown up with two teenage boys and their friends coming in and out. I now have a grandson that loves to play with him. My friends and relatives come and go without any problems. He clearly only does this when he either reads that I think something is not quite right, or when he senses it himself. I've never figured out if it's a cue I give, but I think it may be. I didn't like one of my sons girlfriend's very much and neither did he so my husband thinks he's reading my emotions.