A psychosomatic response was a reflex that was triggered by an incorrect belief or stress.
In 2370, Geordi La Forge began coughing while moving through smoke during his remote inspection of the USS Raman while using an interface suit and its corresponding probe. Doctor Beverly Crusher described his coughing as a psychosomatic response to seeing the gases as though he were actually encountering them physically. La Forge explained that when he saw the smoke, he couldn't help coughing. (TNG: "Interface")
In 2372, Doctor Julian Bashir attributed Elim Garak's nosebleed to a psychosomatic response. He also listed several known psychosomatic responses, such as changes in vital signs and spontaneous tumor growth. When Worf asked if further more serious injuries were possible, Bashir replied that a broken bone was unlikely, but stoppage of his heart or bursting a blood vessel in his brain was possible. (DS9: "Things Past")