This sounds like adrenaline to me. Fight or flight reflex causing you to panic and freeze up due to the unusual feeling of a fast adrenaline flow.
Try breathing slowly and deeply through your nose when it happens, and tell yourself that you can handle this adrenaline, and ask for more (as my book on it says, sounds silly but actually helps)
Then just keep busy until it passes. The important part is to accept it instead of trying to fight it.
If it's not fight-or-flight then it might be linked to stress elsewhere in your life, or you might be nervous about the outcome of this or any similar confrontation.
Please tell me if it helps.
My first post btw.
Just had to try and help you...