The Tagline is a gross misrepresentation of statistics. The actual estimate of awarness during anesthesia is 1:14000 for high risk patients to as low as 1:42000.
Capital-investment firm chief Clay Beresford (Christensen) is in love with a woman named Sam (Alba) but is unwilling to tell his mother (Olin) of their relationship. We later find out this is due to Sam being his mother's personal assistant. Clay suffers from a heart condition that requires a heart transplant to be carried out by Dr. Jack Harper (Howard) who had previously saved his life and is now his good friend. His mother and her famous surgeon boyfriend try to dissuade him from going through the operation with a team of surgeons that have so many malpractice suits pending. Because of his mother's intrusion in his decision to have his friend perform the operation, it seems that Clay begins to grow distant from his mother and eventually discloses his relationship with his fiance Sam. Clay's mother does not take kindly to Clay's haste and asks him to wait until he is older than his 22 years.
Clay becomes upset and leaves with his fiance. He asks Dr. Harper to arrange a wedding for him and Sam immediately. They marry in a private ceremony in a church at midnight. After the wedding, Clay is notified by the hospital that it's time to perform the operation. Clay then goes to the hospital to get surgery. His mother tries to dissuade him again and refer him to a better clinic and a more experienced doctor. Clay brushes aside their concerns as attempts to interfere with his friendships and proceeds with his original plans, touching upon the point that "he trusts Jack". However, during surgery Clay encounters "anesthetic awareness", which is a condition that renders a patient completely paralyzed, unable to move or speak, but able to hear the doctors, and more importantly, still feel pain. To escape the excruciating pain of having his chest sliced open and his ribs separated, Clay attempts to focus on Sam, now his wife, and eventually has an out-of-body experience and uncovers a murder plot against him. (Spoiler warning).
During his outerbody experience Clay discovers that Dr. Harper, one other surgeon and a nurse are in on a plot to inject his transplanted heart with a chemical that will cause it to be rejected upon transplantation. Dr. Harper has second thoughts at which point Clay's new wife Sam comes in. Apparantly she is a main part of the whole scheme. The doctors want Clay to die because now that he and Sam are married, his millions will go to her, and in turn, pay for all the hospital's malpractice suits (later we find out that Sam used to be a nurse there). She proceeds to encourage him and even coerces him to go through with the plan and inject the transplanted heart. The heart if rejected would cause Clay to die because he (like his mother is O negative - a rare blood type) will not find a transplant in time.
In the operating room one of the conspirator's fails to show up and a seemingly inept anesthesiologist with an apparent drinking problem shows up to replace him. Meanwhile Clay's mother anxiously awaits for the results of the operation. Sam tries to win over her mother in law during her vulnerable moment. One of the surgeons makes a move on Sam since he feels he had seen her before.
During his out of body experience Clay discovers and remembers things about his wife that point to her deceipt. Meanwhile as Sam is shuttling between the operating room and consoling (winning over) Clay's mother she forgets her purse in the waiting room. Clay's mother growing suspicious of Clay's newly wed wife looks through her purse and discovers that Sam was a nurse before she became her assistant. Clay during his out of body experience finds that Sam worked at the hospital and worked under Dr. Harper. He is dejected and accepting his fate walks (during his out of body experience) to his own home and awaits death.
Clay's mother begins piecing together the situation, based on Sam's behavior and conversations, and finally gets a notion of what's going on. Upon discovering the truth, she takes an overdose of some of her son's medicine, and calls her boyfriend, the prestigious surgeon, and tells him the whole situation. She tells him to come save her son. Her surgeon boyfriend returns to evict Dr. Harper, and, upon seeing the mother's death, realises that she overdosed so that he could save her son (they had the same rare blood type). He then transplants the mother's heart into the son. Dr. Harper and his associates are arrested.
As the transplant is complete Clay refuses to leave "limbo" since he has nothing left in the outside world after the death of his mother. His mother then proceeds to remind Clay that limbo with his mother and an afterlife with his father may not be that ideal. She reminds him that his father was an addict who was abusive to his son. During one such quarrel she had accidentally murdered her own husband as he was about to harm a young Clay. Dr. Harper continues to narrarate the story, noting that Clay eventually had his revenge. Clay then "wakes up", or "becomes unparalysed", while Dr. Harper's words close the movie with "He is awake".