Hawkins Kevin Francis, 30, pleaded guilty last Friday to one charge of making false threats of terrorist acts, The Strait Times reported.
The court ruled Hawkins was suffering from a relapse of schizophrenia coupled with an episode of major depressive disorder at the time based on a report from the Institute of Mental Health that was presented to court.
However, he knew what he was doing when he made the false bomb threat, a judge said as cited by Channel News Asia.
The incident happened on Oct. 12 on a Scoot flight with 11 crew members and 363 passengers.
Shortly after the seat belt sign was turned off, Hawkins, traveling with his wife, got up from his seat and told a member of the cabin crew that "I have a bomb," South China Morning Post reported.
He told another cabin crew member there was a "bomb" in his trousers pocket, which actually contained his nasal inhaler.
His actions forced the plane to turn back to Singapore an hour into the journey.