An underrecognised masterpiece. Few thrillers really get you on the edge of your seat (frankly, most are dull, cliched and predictable), but this understated gem definitely raises the blood pressure. Also, nicely manipulates your emotions towards the "doctor" as the plot develops.
It deserves much wider recognition which could be aided by release as a DVD...maybe... sometime?
If you fail to be gripped you might want to get the functioning of your nervous system checked out, but possibly not by Dr McGann.