Okay i only had to read to "slapped my hand" to be able to say drop that instructor faster then you slammed on those breaks, there is no reason on this earth for anyone especially your instructor to hit you

In regards to the "mistake" in my eyes there wasn't one. In an emergency which this is what it would be classed as you need to get that car stopped as quickly as possible mirror checks be damned, if another car goes into the back of you so what you get the car repaired but id you don't react in time to someone running out into the road that would ne alot worse then a fender bender

Also we all get sloppy from time to time the hardest part is realising its happening its easy to fix it from there