26 old, Female,married, nonpregnant patient. Since one year ago ,she started complaining of episodes of deep coma ,continue for 30—45 minutes every 20—30 days , no aggravating factors except it's induced only by anger or depression and relieved spontaneously. She has 6 points or less on Glasgow's Coma Scale. No other positive findings. Her BP is115\80#HR is75#HB before 6 months was 13.5 . 1.What are the possible differential diagnosis ??? 2.What types of investigations are required????