If a patient had memories of an abduction which were the product of dreams or stories which were unconsciously created as covers for ritual sexual abuse or other trauma...Mack would have been qualified to identify such.
But a planted liar whose sole purpose was to discredit Mack would be undetectable by a well-meaning psychiatrist.
I think the memories of abduction can be explained by sleep paralysis. A person having sleep paralysis can experience extremely vivid hallucinations, and even think they are getting up and moving around--which is known as out-of-body experience. If you reconcile the physical symptoms of "abductees" (they describe being paralyzed), with the knowledge of the hallucinations, then "alien abduction" becomes very explainable.
In past times, people hallucinated succubi and other forms of supernatural beings. People in other cultures have hallucinations consistent with their culture.
Sleep paralysis is not the symptom of a neurological disorder. I think it is genetic... it has affected every member of my family. About 6% of people are susceptible to it.