When I was growing up I went out to feed our lab/golden mix one evening and he was laying out in the yard sound asleep. It was pretty much the same scenario but I was still about 20-30 ft away when I made a noise (can't remember if I said his name or not). Our fence was down at the time so we had him tied up to a tree. He jumped up and ran at me barking and growling, basically in attack mode. I of course jumped back and yelled at him 2 or 3 times and he snapped out of it between the rope tightening up and me yelling at him. As soon as he realized it was me he calmed down and was happy to see me. I was about 13 when that happened and I have been somewhat cautious when waking up any dog from a deep sleep since then. We talked to the vet about it and he said they can get into such a deep sleep that when they are suddenly awakened their first instinct is defense before anything else. That being said, you still have to be cautious. Ours wouldn't have hurt a fly normally but startling him like that caused a different response.