Micro-choice-based Intervention for Multicausal Fatigue

Inclusion Criteria: \- Experiencing persistent fatigue with a significant impact on daily functioning (Chalder Fatigue- Scale bimodal ≥ 4) Exclusion Criteria: * Have insufficient proficiency in German to complete study-related questionnaires * Lack the cognitive capacity to understand study procedures (e.g. due to dementia) * Present with severe medical conditions that may interfere with participation (e.g., advanced organ failure, uncontrolled inflammatory or autoimmune diseases, or severe psychiatric disorders) * Have active cancer or are currently undergoing cancer treatment * Are deemed incompatible with group participation during the preparation phase, based on a team assessment. Reasons for exclusion based on group incompatibility include: 1. Need for a level of individual therapeutic support that exceeds what can be provided in a group setting; b) Refusal to engage in group-based therapy; c) Personality traits that are considered incompatible with group dynamics; d) Failure to attend the mandatory preparatory webinar (no-show is considered a no-go); e) Other significant reasons as determined by the therapeutic team)