Hi I agree with the above I do not believe your boy has rage symdrome.
I am on a Border Collie forum as well as COL and know of a women who lost her dog recently due to rage syndrome. The symptoms you have described are in no way.
She wasn't until after Bella her dog was PTS that she was informed of RAGE syndrome however she showed tell, tell signs of it.
'Bella made the journey to rainbow bridge today, she has had issues with people, she has shown her teeth and snapped and even bitten my 3 year old nephew, in the last few weeks she has attacked Holly 3 times, two of those times Holly has needed to go to the vet, she just seemed to flip and when she did she felt the need to try and kill, Holly does not fight but Bella did not stop, she would not let go of Holly, it's horrible to see and also horrible for Holly, i have two nephews and what if it had been one of them?'
This is what she posted the day Bella was PTS. Is previous months she has revealed more information on how Bella used to react and the facts are scary, she was cuddley one min, out to literally kill the next.
In my eye's as everyone else has said your boy has reacted in a way most dogs would. RAGE syndrome is a reaction out of no where, uncontrollable and essentially lethal. Your boy is fine.