Patients often report serious difficulties with sleeping while in hospital and this experience of deprivation is even more profound when the patient is in ICU. While there is evidence for the impact of sleep deprivation on cognitive functioning in ICU patients it is only ‘associated’ with the onset of ICU delirium or intrusive hallucinatory experiences. So while we intuitively realise there is a link between sleep and simply feeling better both physically and emotionally, the link does not yet appear to be fully understood or quantified. On the other hand sleep deprivation is acknowledged by Amnesty International to be a means of torture, a process of violence, and in this situation a process of the violence of medicine.
When self- reporting, ICU patients in a study that condensed the findings of a further seven qualitative studies, attributed the feeling of fear or being concerned as the most common cause(71.4%) of their sleep deprivation. The emotional response of the patients to the external physical conditions of being in ICU, the soundscape, the disruption of the diurnal cycle, the experience of frequent medical processes, procedures and interventions were also disruptive and contributed to their perception of fear or being concerned. In addition their individual physical conditions such as being unable to move and/or being unable to talk combined with being in pain could result in a significant level of sleep deprivation. Obviously the impact of some of these causes on ICU patients can be reduced to the extent that it would be reasonably expected to reduce the level of sleep deprivation.
Amnesty International Defining torture https://www.amnesty.org/en/what-we-do/torture/
 Elisa Mattiussi Matteo Danielis Lucia Venuti Marta Vidoni and Alvisa Palese, Intensive and Critical Care Nursing, Volume 53, August 2019, Pages 43-53