Coping After Loss Through Mindfulness in Adults With Prolonged Grief Disorder

The goal of this clinical trial is to pilot the effectiveness of an 8-week standardized Mindfulness Training program to decrease the psychiatric and somatic symptoms of prolonged grief disorder (PGD) and to examine changes in physiological and neuroimaging biomarkers of bereavement-related stress reactivity that are associated with Mindfulness Training in grieving adult patients (men and women, aged 18-60) who are diagnosed with PGD. The main questions it aims to answer are: 1. What is the effectiveness of Mindfulness Training to lower PGD symptom severity? 2. What is the effectiveness of Mindfulness Training on physiological and neuroimaging biomarkers of stress reactivity? 3. What are the potential mechanisms of treatment change of Mindfulness Training? Participants will be: * randomly assigned to immediately receiving an 8-week Mindfulness Training program or after a 12-week waitlist. * assessed for psychiatric and somatic symptoms and for physiological responses during a baseline, midpoint and endpoint visit, and at a one-month follow-up visit. * assessed for functional neuroimaging biomarkers of bereavement-related and general stress reactivity at the baseline and endpoint visits using a script-driven imagery task (which induces bereavement-related stress reactivity during an imagery of a personal situation related to the death compared to imagery of a neutral personal situation), and loud tones stress task (which induces general stress reactivity). Researchers will compare the Mindfulness Training group (which consists of patients with PGD who will receive the Mindfulness Training immediately) with the waitlist control group (which consists of patients with PGD who are waiting on a waitlist to receive the training after the Mindfulness Training group) to investigate if they differ in PGD symptom severity as well as physiological and neuroimaging biomarkers of stress reactivity.