Why does focusing on my heartbeat trigger my fear of death?

When the guide asks me to focus on the sensations of my heart, I suddenly get an overwhelming sense of existential panic and the fear of death. My heart races, and I feel intensely vulnerable. This specific focus, meant to ground me, completely destabilizes me. Is this a common anxiety response to increased physical awareness, or a sign of deeper psychological trauma? My name is Ashok, DOB is 7th February 1993, 7 AM, in Hyderabad.