Ultra-brief Psychological Treatments for Emotional Symptoms and Disorders

The main objective of this randomized clinical trial is to study if various modalities of brief (eight sessions) and ultra-brief (four sessions) transdiagnostic cognitive-behavioral treatment work for decrease emotional symptoms and disorders, as well as to find out which emotional regulation processes and common factor of the intervention itself are involved in the therapeutic improvement. The investigators will compare the interventions of four groups: ultra-brief group treatment (1), brief group treatment (2), ultra-brief individual treatment (3) with the ultra-brief relaxation (control) group. The main questions the study aims to answer are: * Will the brief and ultra-brief treatment formats works better than the relaxation-based control group? * Will results obtained between the brief group therapy group and the ultra-brief group therapy group be similar? * Will the individual ul