Your anxiety from prior events has caused you to memorize your prior concussion symptoms. When you got the haircut, the anxiety caused your brain to call up those memories as if they were real for that moment in time.
Think of those events as flashbacks.

YOU DID NOT SUFFER ANY IMPACTS.

Just an anxiety response.

Think of how your whole body responds when you see somebody impact their head on TV or in a movie. It is fake but your brain plays the whole list of reactions and momentary symptoms.

Guys also experience spasming sensations when they see another guy get hit in the groin.

Flash back with a well memorized set of responses.