Participants will be asked in the morning and in the evening at their self-selected time to evaluate their emotional state through ecological momentary assessment (EMA) and will be prompted to engage in an ER intervention (60% likelihood) or to read health information (40% likelihood). Upon completion they will evaluate the likability and helpfulness of the exercise or the article and re-evaluate their emotional state (post-EMA).

The intervention consists of 20 ER exercises and 20 health facts. The ER intervention is based on different therapeutic approaches targeting various underlying transdiagnostic factors such as rumination, self-referential thoughts etc. The 20 health facts will act as a placebo intervention with no effect on emotion regulation and keep participants engaged in the post-EMA evaluation when they are not randomized to an exercise.

The interventions and the control intervention materials were developed by the research team for the purposes of this study.

The intervention under study includes 5 therapeutic approaches, namely: Positive psychology [PP], Mindfulness, Acceptance and Commitment Therapy [ACT], Breathing and relaxation, and Self-compassion [SC].

The intervention consists of 4 core features:

(i) monitoring through filling in EMAs assessing participants emotional states

(ii) feedback through visualization of participant emotional states upon every completion of the EMAs

(iii) exercises targeting different emotion regulation skills [i.e., upregulation of positive affect, mindfulness, cognitive defusion, breathing and relaxation, self-compassion) and health facts (i.e., control intervention) describing health information including nutrition, exercise, sleeping habits.

(iv) psychoeducative articles describing the 5 therapeutic approaches (PP, ACT, Mindfulness, Breathing and Relaxation, SC)](streamdown:incomplete-link)

Participants will be asked to evaluate seven emotional states before and after engaging in the ER intervention or control intervention by answering the question: "How [affect (e.g., happy)] do you feel at the moment?" Each of 7 emotional states is evaluated on a scale from 1 [Not at all] to 5 [Extremely]. The emotional states are combined into 2 categories of affect: negative (stressed, frustrated, sad, fatigued) and positive (happy, energetic, relaxed).

Changes in the momentary emotional states (i.e., positive and negative affect) will be evaluated by looking at the responses on the pre and post EMA in the relation to whether a participant received an ER intervention or health information.

When randomized to CD exercise, participants will be asked to evaluate their self-selected unhelpful thought answering the following questions on a scale from 1 (not at all uncomfortable/believable) to 100 (extremely uncomfortable / believable) before and after the exercise:

"How uncomfortable is the thought?" "How believable (true) is the thought?"

The effects of CD exercises will be assessed by comparing the pre and post scores on the two thought parameters.

Objective engagement patterns with the intervention will be assessed using descriptive statistics of engagement metrics (i.e., exercise completion rates, average time spent, and times of the day where participants completed the exercises) per exercise and exercise category. In addition, a correlational analysis will be used to evaluate whether there is a relationship between time of the day and exercise completion rates.

A correlational analysis will be used to evaluate whether there is a relationship between the time of the day participants engaged in an exercise and exercise completion rates.

ER skills will be measured with the Emotion Regulation Skills Questionnaire [ERSQ] that evaluates seven types of ER skills: awareness, sensation, clarity, understanding, acceptance, tolerance, compassionate self-support, readiness to confront distressing situations, and modification of negative emotions. The 27 items are rated on a scale from 0 [ not at all ] to 4 [ almost always ]. Higher scores on the ERSQ subscales and the overall ERSQ score indicate higher ER skills.