During a turn after takeoff, the pilot reported the control stick suddenly 'snapped back' to the full nose up position. The aircraft was at about 300 ft AGL when it stalled. The pilot who was in the back seat was unable to recover before ground impact. After the accident, the pilot reported that his passenger was in a 'highly excited state' before takeoff and wanted to take off even though the weather was not good along their route of flight. The pilot also said the passenger in the front seat disappeared from his view as the aircraft reached 300 ft. After the control stick episode, the passenger's head reappeared. Post crash inspection of the aircraft revealed no malfunctions of the controls or engine. Three drugs were found in the baggage of the passenger: Dexedrine 5mg, Transderm-Scop 4's, and Compazine 5 mg. These were self-prescribed by the doctor passenger for air sickness but had side effects of overstimulation, restlessness, dizziness, jitteriness, and insomnia.