Baseline phase ('A'): Measurements collected in a pen-and-paper diary four times a day (morning, afternoon, evening and night) over one week for the primary outcome (occurrence of intrusive memories of trauma). Individual baseline phases will be used as control periods.

Intervention phase ('B'): A one-session intervention with a researcher including a simple cognitive task (a memory cue, 10 minutes time gap and ca. 20 minutes of Tetris game-play) followed by instructions to engage in the task self-guided over the subsequent week. Measurements collected in a pen-and-paper diary four times a day over one week following the intervention for the primary outcome (occurrence of intrusive memories of trauma).

A one-session intervention with a researcher including a simple cognitive task (a memory cue, 10 minutes time gap and ca. 20 minutes of Tetris game play) with instructions to engage in the task self-guided in the subsequent week.

Number of intrusive memories of traumatic event recorded by participants in a diary daily (morning, afternoon, evening and night) for one week during the baseline phase and one week during the intervention phase.

Feasibility and Acceptability of the intervention was assessed with 10 self-rated items, e.g. "Would you recommend playing Tetris to a friend?". Scores could range from 0 - 10 with higher scores indicating greater acceptability/feasibility. Two items had open-ended follow-up questions: "How did you feel about playing Tetris after you had an intrusive memory?" and "Why"? or "How much would you prefer an intervention that is delivered by a computer/smartphone compared to seeing a doctor/psychologist in person?" and "Why"?