The number of patients discharged alive from the ICU is increasing due to the remarkable progress of medical care. Nevertheless, a growing concern is that many ICU survivors subsequently develop mental health impairments. Recently, it has become clear that the memories formed during a patient’s ICU stay are a risk factor for subsequent mental health impairment. Patient memories can be classified into memories of factual events, memories of feelings, and delusional memories. Delusional memories are reported by 26-73% of ICU survivors and can be difficult to forget. Delusional memories are also thought to be correlated with mental health impairment, such as anxiety, depression, posttraumatic stress disorder (PTSD), a lower QOL, and failure to return to work. To support the formation of beneficial memories in patients, clinicians should help patients to construct appropriate memories during their ICU stay, to restructure memories after their discharge from the ICU, and to avoid preserving delusional memories. However, further research is required in this field. Understanding how unpleasant memories can lead to long-term disturbances in patients, even if the memories are not factual, and providing follow-up opportunities for patients to talk about their experiences after they have left the ICU may be necessary.