 The film is based on a real condition called "awareness during  surgery" that leaves patients aware but paralyzed during their  operation. When patients first made claims of levels of awareness  during their operations from hearing surgeons conversations to  feeling the pain of their surgery doctors wrote off their  experiences as hallucinations or dreams. Later tests proved the  condition was real and current estimates suggest it affects 40,000  to 140,000 patients each year. Newly introduced monitoring systems  have been shown to reduce the likelihood of such occurrences by 80%.