My first thought was why were you down on the floor with him?
I haven't followed the whole story on this dog, but as a general matter I would have thought that dog on floor, people on furniture would have been cardinal rule and that someone on this list would have already told you that.
I don't generally start looking for mysterious switches until the basics of how to manage an ordinary large usually dominant breed are being followed. And that one failure--to follow the dogs on floor, people on furniture rule, would suggest to me that much else in basic dog management is not being followed thus for me it would not be a surprise to see a lack of respect from the dog developing. Wouldn't myself think of hormonal causes for aggression before the basics of respectful relationship have been established either.
