Inclusion criteria:  Aged 18 or above. Able to read, write and speak in English. Worked in a clinical role in an NHS Intensive Care Unit or equivalent during the COVID-19 pandemic. Experienced at least one traumatic event related to their work during the COVID-19 pandemic, meeting criterion A of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) criteria for Post-Traumatic Stress Disorder (PTSD): "exposure to actual or threatened death, serious injury, or sexual violence" by "directly experiencing the traumatic event(s)" or "witnessing, in person, the event(s) as it occurred to others" Have intrusive memories of the traumatic event(s). Experienced at least three intrusive memories in the week prior to screening. Have internet access. Willing and able to provide informed consent and complete study procedures (including briefly listing their intrusive memories (without going into any detail), and playing the brief digital imagery-competing task with particular mental rotation instructions, and completing an online intrusive memory diary). Willing and able to be contacted by the research team during the study period.  Exclusion criteria:  • Have fewer than three intrusive memories during the run-in week.  We will not exclude those undergoing other treatment for PTSD or its symptoms, so the study is as inclusive as possible to meet the challenges ICU staff are facing during the COVID-19 pandemic.