KOLKATA: A bright Class-XII student of South Point High School was found hanging from the ceiling fan of his room, locked from inside, at Kalighat on Monday night, hours after he had told his mother to let him be for some time as he was preparing a chemistry lesson. The parents said the boy was undergoing treatment for bipolar disorder, a mental disease that deals with extreme shifts in mood ranging from mania to depression.The boy's mother said he had been obsessed with his cellphone for the past four days since he had watched the horror movie 'Annabelle: Creation' with his friends last Wednesday after bunking school. Police have not found any suicide note but suspect he had possibly hung himself out of depression.Around 9pm on Monday, Srijan Chowdhury, 17, asked his mother for her pho ne and told her he was going to his room to study. His mother, a law officer with Metro Railways , was watching TV in the adjacent room. An hour later, when he did not reply to knocks on the door after dinner was served, she called neighbours who forced through the door to find Srijan hanging from the ceiling fan. He was taken to Ramakrishna Mission Seva Pratisthan where he was declared dead. His father, a CESC engineer, was not at home at the time.The family has not lodged any complaint in the case so far. Srijan's mother suspected the suicide could have been triggered by either the horror movie or something he was doing with the cellphone but psy chiatrists, E including including the one who had once treated him, said suicidal tendency is common among some patients with bipolar disorder.“It is a chronic condition of extreme shifts in mood ranging from high to low. During mania, an individual behaves or feels abnormally energetic, happy and even does mimicry .During periods of depression, they may be crying, have a negative outlook on life, and even commit suicide,“ said psychiatrist Jay Ranjan Ram, who had treated the boy when the disease was detected eight years ago.Srijan's mother Shukla Chaudhuri said on Tuesday that two days ago, Srijan had told her he had watched a horror movie with friends and learned those who watch it tended to commit suicide. “I asked him not to think about the movie and concentrate on his studies. But he had been behaving a bit abnormally since the day,“ she said.“We are devastated by the news. The class teacher of Srijan remembers interacting with him even on Monday. His medical records and medication details were kept with the school,“ said school trustee Krishna Damani.