OASIS is a 5-item self-report questionnaire measuring anxiety symptom severity (5-point Likert scale ranging from 0 to 4) with higher scores indicating greater anxiety-related severity and impairment. The total score is the sum of all 5 items, and ranges from 0 to 20. OASIS will be used to measure change, from pre-to post-intervention, in anxiety.

PHQ-9 is a 9-item self-report questionnaire measuring depression symptom severity (4-point Likert scale ranging from 0 to 3) with higher scores indicating greater depression symptom severity. The total score is the sum of all 9 items, and ranges from 0 to 27. PHQ-9 will be used to measure change, from pre-to post-intervention, in depression.

PTQ is a 15-items self-report questionnaire to measuring negative thinking that is repetitive, unproductive, difficult to disengage from and that captures mental capacity (5-point Likert-scale ranging from 0 to 4) with higher scores indicating greater repetitive thinking. The total score is the sum of all 15 items, and ranges from 0 to 60. PTQ will be used to measure change, from pre-to post-intervention, in negative repetitive thinking.

MWQ is a 5-item self-report questionnaire measuring levels of mind-wandering (6-point Likert scale ranging from 1 to 6) with higher scores indicating greater levels of mind wandering. The total score is the sum of all 5 items, and ranges from 5 to 30. MWQ will be used to measure change, from pre-to post-intervention, in mind-wandering.

The brooding subscale of the RRS is a 5-items self-report questionnaire measuring levels of brooding (4-point Likert scale ranging from 1 to 4) with higher scores indicating greater levels of brooding. The total score is the sum of all 5 items, and ranges from 5 to 20. RRS will be used to measure change, from pre-to post-intervention, in rumination/brooding.

FFMQ is a 39-item self-report questionnaire measuring 5 facets of trait mindfulness (5-point Likert scale ranging from 1 to 5) with higher scores indicating greater levels of trait mindfulness. The FFMQ includes 5 subscales measuring facets of mindfulness: observing, describing, acting with awareness, non-judging of experience, and non-reactivity to inner experience. Each subscale score is the sum of its items. FFMQ will be used to measure change, from pre-to post-intervention, in facets of trait mindfulness.

MAIA is a 32 -item self-report questionnaire measuring 8 dimensions of interoceptive awareness (6-point Likert scale ranging from 0 to 5) with higher scores indicating greater levels of interoceptive awareness. The MAIA includes 8 subscales measuring dimensions of interoceptive awareness: noticing, not-distracting, not-worrying, attention regulation, emotional awareness, self-regulation, body listening, and trusting. Each subscale score is the sum of its items. MAIA will be used to measure change, from pre-to post-intervention, in dimensions of interoceptive awareness.

SOCS-S is a 20-item self-report questionnaire measuring 5 different dimensions of self-compassion (5-point Likert scale ranging from 1 to 5) with higher scores indicating greater levels of self-compassion. The SOCS-S includes 5 subscales measuring dimensions of self-compassion: recognizing suffering, understanding the universality of suffering, feeling for the person suffering, tolerating uncomfortable feelings, and motivation to act/acting to alleviate suffering. Each subscale score is the sum of its items. SOC-S will be used to measure change, from pre-to post-intervention, in dimensions of self-compassion.

MPod-t is a 15-item self-report questionnaire measuring trait levels of the 3 metacognitive processes of decentering (5-point Likert scale ranging from 1 to 5), with higher scores indicating greater levels of decentering. The MPoD-t includes 3 subscales measuring the metacognitive processes of decentering: meta-awareness, disidentification from internal experience, and non-reactivity to internal experience. Each subscale score is the sum of its items. MPod-t will be used to measure change, from pre-to post-intervention, in the metacognitive processes of decentering.

NAS-7 is a 7-item self-report questionnaire measuring nonattachment (6-point Likert scale ranging from 1 to 6) with higher scores indicating greater levels of nonattachment. The total score is the sum of all 7 items, and ranges from 7 to 42. NAS-7 will be used to measure change, from pre-to post-intervention, in nonattachment.

DERS is a 16-item self-report questionnaire measuring 5 dimensions of difficulties in emotion regulation (5-point Likert scale ranging from 1 to 5) with higher scores indicating greater difficulties with emotion regulation. The DERS-16 includes 5 subscales measuring dimensions of difficulties in emotion regulation: lack of emotional clarity, difficulties engaging in goal-directed behavior, impulse control difficulties, limited access to effective emotion regulation strategies, nonacceptance of emotional responses. Each subscale score is the sum of its items. DERS-16 will be used to measure change, from pre-to post-intervention, in difficulties in emotion regulation.

The trait I-PANAS-SF is a 10-item self-report questionnaire measuring trait positive and negative affect (5-point Likert scale ranging from 1 to 5) with higher scores indicating greater positive and negative affect. The I-PANAS-SF includes 2 subscales, one measuring positive affect and the other measuring negative affect. Each subscale score is the sum of its items. PANAS-SF will be used to measure change, from pre-to post-intervention, in negative and positive affect.

SMS is a 21-item self-report questionnaire measuring state mindful awareness of body and mind (5-point Likert-type scale ranging from 1 to 5) during the MAT mindfulness meditation, with higher scores indicating greater state mindfulness. The SMS total score is the sum of all 21 items, and ranges from 21 to 105. It includes 2 subscales, one measuring mindful awareness of body and the other measuring mindful awareness of mind. Each subscale score is the sum of its items. SMS will be used to measure change, from pre-to post-intervention, in state mindfulness during the MAT mindfulness meditation.

The curiosity subscale subscale of the TMS is a 6-item self-report questionnaire measuring state curiosity towards present moment experience (5-point Likert-type scale ranging from 0 to 4) during the MAT mindfulness meditation, with higher scores indicating greater state curiosity. The TMS-C score is the sum of all 6 items, and ranges from 0 to 24. TMS-C will be used to measure change, from pre-to post-intervention, in state curiosity during the MAT mindfulness meditation.

MPod-s is a 3-item self-report questionnaire measuring state levels of the 3 metacognitive processes of decentering (11-point Likert scale ranging from 0 to 10) with higher scores indicating greater levels of decentering (minimum scale score 0 and maximum scale score 10). Each of the 3 MPoD-s items measures a metacognitive process of decentering: meta-awareness, disidentification from internal experience, and non-reactivity to internal experience. MPod-s will be used to measure change, from pre-to post-intervention, in state decentering during the MAT mindfulness meditation.

State I-PANAS-SF is a 10-item self-report questionnaire measuring state positive and negative affect (5-point Likert scale ranging from 1 to 5) during the MAT mindfulness meditation, with higher scores indicating greater state positive and negative affect. The I-PANAS-SF includes 2 subscales, one measuring positive affect and the other measuring negative affect. Each subscale score is the sum of its items. State I-PANAS-SF will be used to measure change, from pre-to post-intervention, in state positive and negative affect during the MAT mindfulness meditation.

11 experience sampling item measuring the following mindful awareness processes (9-point Likert scale ranging from 1 to 9) during the MAT mindfulness meditation: mindful awareness of the breath, body, mind, pleasant and unpleasant hedonic tone, as well as meta-awareness, mindful awareness time, sustained mindful awareness, and latency to re-engagement in mindful awareness, and mindful awareness of change. Higher scores indicate greater levels of mindful awareness. Experience sampling will be used to measure change, from pre-to post-intervention, in state mindful awareness processes during the MAT mindfulness meditation.

9 experience sampling item measuring the following attitudinal qualities of mindful awareness (9-point Likert scale ranging from 1 to 9) during the MAT mindfulness meditation: curiosity about bodily and mental experience, distance and (dis)Identification with internal experience, hedonic-based desire of pleasant and unpleasant experience (non-equanimity), willingness, and experiential avoidance. Higher scores indicate greater levels of each attitudinal quality. Experience sampling will be used to measure change, from pre-to post-intervention, in attitudinal qualities of mindful awareness during the MAT mindfulness meditation.

9 experience sampling item measuring the following phenomenological states (9-point Likert scale ranging from 1 to 9) during the MAT mindfulness meditation: fatigue, alertness, falling asleep, effort, boredom, enjoyment, relaxation, and mind-wandering frequency and duration. Higher scores indicate greater levels of each phenomenological state. Experience sampling will be used to measure change, from pre-to post-intervention, in phenomenological states during the MAT mindfulness meditation.

PMES is a 32-item self-report questionnaire measuring the occurrence of 32 types of peak experiences (unusual and uncommon experiences) during the retreat/last week ("yes" or "no"), their frequencies (open ended number), duration (open ended number), and degree of hedonic tone (9-point Likert scale ranging from -4 to +4). Positive hedonic tone scores indicate pleasant hedonic tone, zero scores indicate neutral hedonic tone, negative scores indicate unpleasant hedonic tone. The PMES items relate to 6 domains of peak experiences: positive emotions, negative emotions, perception, altered states of consciousness, dissociation, and insight.

I-PMES is a self-report questionnaire measuring the positive and negative impact of peak experiences that participants had during the retreat, on participant's lives after the retreat (two 5-point Likert scales for each experience: positive impact ranging from 0 to +4, negative impact ranging from 0 to -4). The number of items in this scale varies between participants as they are only asked to rate the impact of peak experiences they indicated in the PMES that they had during the retreat. Only participants in the mindfulness meditation retreat condition will complete this measure.