6 self-rated items measuring the frequency of unwanted memories of the trauma in the previous week on a 7-point scale (from never to many times a day) and the level of distress, nowness, reliving, disconnectedness and whether different triggers are associated with the unwanted memories of the trauma on a 11-point scale (from 0 to 100). High scores indicate more unwanted memories, higher levels of distress/nowness/reliving/disconnectedness and more different triggers.

The PCL-5 is a short 20-item self-report scale used to assess the severity of PTSD symptoms corresponding to the DSM-5 criteria for PTSD. Symptoms are rated from 0-4. Higher scores indicate greater severity.

The PHQ-9 is a 9-item self-report measure of depression symptoms and the severity of those symptoms. Each item is scored from 0 (i.e., not at all) to 3 (i.e., nearly every day).

The GAD-7 is a brief self-report questionnaire designed as a screening tool for symptoms of general anxiety disorder and their severity. Each item is scored from 0 (i.e., not at all) to 3 (i.e., nearly every day).

The SDS is a self-report questionnaire which is designed to assess functional impairment across three domains: (1) Work/school, (2) social, and (3) family life. These domains are measured on an 11-point scale which ranges from 0 (i.e., not at all) to 10 (i.e., extremely). The scale will be adjusted to assess impairment associated with intrusive memories.

The WHODAS 2.0 is a 12-item self-rated questionnaire measuring difficulties due to health conditions, including mental or emotional problems (with reference to study event). Scores range from 1 ("none") to 5 ("extremely/cannot do"). The maximum score of the WHODAS is 60; lower scores indicate better functioning.

Six self-rated items to assess the impact of intrusive memories on concentration, sleep, and stress in the past week. 2 items assessing concentration difficulties in general and due to intrusive memories (11-point scale; high scores indicating more difficulties). 2 items assessing sleep disturbances due to intrusive memories (11-point scale; higher scores indicating more sleep disturbance); and 1 item assessing to what degree intrusive memories affected stress levels (0 = not at all; 10 = affected very much).

One item assessing for how long intrusive memories disrupted concentration on average on a 6-point scale (0 = <1 minute - 6 = > 60 minutes)

Two questions assessing the impact intrusive memories have on functioning in daily life. One question is open-ended: "Have the intrusive memories affected your ability to function in your daily life in the past week? If yes, how?" and one question is self-rated: "Have the intrusive memories affected your ability to function in your daily life?" (11-point scale, higher score indicate greater impact on functioning.)

Two items both rated on an 11-point scale: 1. "During the last week, how distressing were your intrusive memories (0 = not at all; 10 = very distressing). 2. During the last week, how vivid were your intrusive memories (0 = not at all; 10= very vivid). Administered as part of the intrusive memory diary.

A single item measuring perceived health status on a seven-point scale (from very good to very bad). Higher scores indicate better health.

Two self-rated items: Item 1 measures the extent of being troubled by poor sleep (with reference to study event) on a 5-point scale (from not at all to very much), and item 2 measures the number of nights in the week with sleep problems on 5 point scale (from 0-1 to 5-7 nights). Each 5-point scale is reverse scored (0 - 4) then summed. Possible total scores range from 0 - 8, with higher values indicative of better sleep.

Two bespoke items measuring the total number and the number of full work days of sick leave the participant has taken over the past 4 weeks.

8 self-report items (5-point scale from 1 to 5) measuring time perspective on three subscales: past perspective (items 3, 5, 7), present perspective (items 1, 8) and future perspective (items 2, 4, 6). Item scores for each subscale will be summed. Higher values indicate higher levels of past/present/future time perspective.

A free text response field asking to imagine a future self identity. Then a free text response field to describe a mental image of this identity, 2 items measuring vividness (from 1 "not vivid at all" to 10 "very vivid") and positivity (from 1 "very negative" to 10 "very positive") of that image on a 10-point scale and 1 item measuring the perspective of viewing that mental image ("through own eyes" or "as if seeing oneself") before and after the traumatic event(s). Higher scores on rating scales indicate higher levels of vividness/positivity.

Two self-report items: "How many times did you manage to play Tetris after you experienced an intrusive memory?" (12-point scale: 0-10 or more than 10). If 1 or more is selected, participant is also asked: "Which of your intrusive memories did you target when you played on your own?" (open-ended question)

Adherence to the intrusion diary assessed with 1 item: "How accurately did you fill out the diary?" (0= not at all; 10 = very accurately)

Feasibility and acceptability of the intervention assessed with two self-rated items, "Would you recommend playing Tetris to a friend?" and "Do you consider gameplay to be an acceptable way to reduce the daily frequency of intrusive memories?". Scores could range from 0 - 10 with higher scores indicating greater acceptability/feasibility.

Feasibility and acceptability of the intervention assessed with two open-ended questions: 1. "How did you feel about playing Tetris after you had an intrusive memory?" 2. "Did you find the intervention helpful? If yes, how?"

Prior to completing the intervention, participants provide 5 ratings of treatment expectancy as well as the degree to which they found the rationale for treatment credible; wording adapted to fit the current study.