Review Question - QID 216633

A 14-year-old boy presents to his pediatrician with a 2-month history of intermittent arm and leg spasms. He says that the spasms usually occur after he wakes up as he is getting ready for school, and consist of disorganized jerking motions that stop after a few minutes. He has also noticed that they occur when he stays up late to cram last minute for exams. He has not noticed any other symptoms. He has no medical history and takes no medications. He recently started experimenting with alcohol and marijuana that one of his friends has been stealing from their parents. His temperature is 98.6°F (37.0°C), blood pressure is 115/70 mmHg, pulse is 70/min, and respirations are 12/min. Physical exam reveals a healthy child. Which of the following is the most likely cause of this patient's symptoms?