Have a father who’s a pediatrician with his office in the first floor of your house, the sound of crying babies coming up through the floor boards, some patients so afraid they run out the door screaming, have to be chased down.  

Live in a state of perpetual longing for Dad’s approval.  Live in a time when boundaries and roles were not such an issue.  Your father is your pediatrician.  Hear him joke about scared kids who make a fuss over an injection that takes just a moment, praise those who are stoic.  
Stay out beyond curfew on the deadline date for requisite camp shots, DPT and MMR.   Get growled at by your dad who comes down to the first floor in his boxers, turns on the lights and pulls the serum from the fridge and the syringes from the sterilizer.      

Your stomach turns as he swabs your arm with alcohol.  Don’t look, don’t cry, be the strongest silent soldier you can be.   Maybe still not breathing when he says Done, tells you to go write it on your chart, and heads back upstairs to bed.  

Plunk yourself in the swivel chair at the reception desk, pull your record, a 5 x 7 card filled with your father’s fountain pen scratches.  The words on the card blur.  Things go black, your cheek and shoulder slam the linoleum, the chair skids, crashes the opposite wall.  

The first but not the only time, you learn it is your vagal nerve, the longest cranial nerve in the body.  It can overreact to triggers, the brain signaling the heart rate and blood pressure to suddenly drop.  Yes, this is the opposite of gearing up more usefully for fight or flight.  

As an adult, my doctor relieves my wimpy heart with this translation: Your father’s daughter, you were trying too, too hard to be brave.