Dynamic Context Modeling for Longitudinal Mental Health Monitoring under Distribution Shift

Mobile and wearable sensing offer a scalable pathway to longitudinal mental health monitoring, yet accurate prediction remains limited by two fundamental forms of distribution shift in human behavior. The first arises across users, where similar sensor patterns can carry different clinical meanings, a phenomenon we call inter-subject heterogeneity. The second arises within a single user, where behavioral baselines themselves evolve over time, producing intra-subject behavioral drift. In this domain, ground-truth labels come from Ecological Momentary Assessment (EMA), brief self-reports collected in everyday life that are intrusive and inherently sparse. As a result, approaches that address these distribution shifts by updating model parameters are difficult to apply. To address this gap, we propose DyCon (Dynamic Context Modeling), a dual-loop framework that personalizes by building and evolving a separate natural-language personal context for each user, without updating any model parameters. Within each session, a momentary refinement loop restructures this personal context to resolve inter-subject heterogeneity. Across sessions, a longitudinal update loop integrates only validated insights to track intra-subject behavioral drift. Extensive experiments on four public benchmarks (GLOBEM, PMData, StudentLife, LifeSnaps) show that DyCon consistently outperforms baseline methods, particularly under sparse supervision and behavioral drift. Our results suggest that evolving an explicit personal context offers a practical pathway for longitudinal personalization in real-world health monitoring.