Even though Jamie is nearly 30 years old, once a year, she reverts to behaving like an adolescent.“When I go home for the holidays, it feels like I never left. My mom still nags at me about my weight, and my older sister still competes with me for our parents’ approval,” said Jamie. “Last Christmas Eve, as I reached for a piece of pecan pie, my mom rolled her eyes and criticised me for eating ‘carbs.’ I got so frustrated that I pushed away my plate, stomped upstairs and hid in what used to be my childhood bedroom, because I couldn't take landing smack back in the dysfunction of my youth."Sound familiar? This phenomenon of acting like your teenage self around your family is actually pretty common. Jamie, like many people during the holidays, is suffering from “holiday regression” — a standard emotional response to the stressful dynamics that pop up between family members at this time of year. But while this reaction is common, that doesn’t mean it doesn’t confuse the hell out of people.“Even when I am stressed out at work or angry with my boyfriend, I don’t respond immaturely. But back at home, I turn into a pouting teenager all over again,” Jamie said.The term “ regression ” can be traced back to our psychological forefather, Sigmund Freud, who claimed that it’s a defence mechanism that protects us from feeling uncomfortable emotions, such as anger, sadness, and shame. It springs into action when we face tense situations — like those holiday family gatherings — because even when we've physically moved out of our childhood homes, we never actually leave our family dysfunction behind.“I’ve always felt like my mom projects her body-image issues onto me, but I don’t think that she realises it,” Jamie said. “It makes me feel trapped, and so I still react when she judges me.”It might be helpful to think of our family configurations like puzzles — each member has a set role that keeps the unit functioning. Family therapists refer to this process as “ equilibrium ,” which is the way that a family finds its emotional balance. Take Jamie’s family: She said that she’s the emotional one, her sister is the perfectionist, her mom is the worrier, and her dad’s the laid-back one.“Even though I moved out over 10 years ago, we still identify with these labels,” Jamie said.Another way to understand our regressive behaviour during the holidays is to view it through the lens of classical conditioning. It's a behavioural theory of psychology that says that there are stimuli that trigger old memories, which can spark regressive behaviours. These stimuli might include eating dinner around your childhood dining table or sleeping in your childhood bed or simply listening to an old song. Each of these experiences can catapult you back through time to a place where you felt more vulnerable.