Recently my son s girlfriend passed away. No cause has been found but there are plenty of questions. She lost a lot of weight over the last 7 months (approx. 50 pounds). A lot of people thought it could possibly be an eating disorder . Her s/s were - rapid heart rate, weight loss, excessive thirst, muscle weakness and tiredness, but the most important sign was low potassium levels. Was it possible that this was diabetes insipidus ... She was 17 years old and died in her sleep.