It's like when you go to the doctor and he threatens you that you may have to take a shot (with a rather large seringe) if your symptoms persist.... almost always the patient is instanly healed as if by miracle.

EDIT: But seriously now, psychology plays a major role on a patient's recovery. I remember when I was younger and I was feeling really bad and my parents took me to the hospital, the doctors said that I needed to stay there. I was dead scared of hospitals and when I heard that I suddenly felt better. No more vomiting, drowsiness or anything. I felt great.
(Still though I was forced to stay under observation for a week... lol)