Why this doctor killed family and ended his life?

Gurgaon: A doctor allegedly killed his wife and two children and later committed suicide at his flat in Sector 49 Uppal Southend here, police said Monday.
According to the police, the incident took place on Sunday night. The locals reported the matter to police on Monday when they did not spot the family outside since morning.
The police found all the four family members lying dead on the floor.
Prima facie, it appears Prakash Singh (55) killed his wife Sonu Singh (50), daughter Aditi (22) and son Aditya (13) with a sharp weapon while they were sleeping, they said.
Prakash later hanged himself from the ceiling fan, police said.
Prakash, a PhD degree holder, worked with a Hyderabad-based chemical factory. He was staying in Gurgaon from the last eight years. He was a native of Varanasi in Uttar Pradesh.
His wife ran her own school in Gurgaon, they said. All the family members, except Prakash, had multiple stab wounds. Their throats were also slit, police said.
A suicide note reportedly written by Prakash was found from the spot in which the doctor said that “he was not able to handle his family”.
“We are examining the note with the help of handwriting experts to ascertain whether the letter was written by the doctor or someone else,” a police official said.
The bodies have been sent for postmortem, he added.