Why does imagining a warm glow in Metta cause vulnerability and explosive anxiety?

When I am asked to imagine a warm, golden glow around my heart, and glowing, I experience a highly vulnerable feeling, as though my emotional armour has been disarmed and taken away too fast. Such a sense of vulnerability is then succeeded by an explosion of anxiety. I guess this has something to do with some past trauma when being emotionally open exposed that person to a lot of pain. Does this naked exposure play a role in the healing process? My name is Sneha, born on 8th April 1995. Time: 5:20 PM. Location: Hyderabad.