A mother gave her brain-damaged son a lethal heroin injection in order to end his life "peacefully and painlessly", a court has heard.
Frances Inglis, 57, of Dagenham, Essex, denied murdering Thomas Inglis, 22, on 21 November 2008 and is challenging her conviction.
Her barrister told the Court of Appeal she believed her son was in "constant pain".
She was ordered to serve a minimum term of nine years in January.
She was found guilty of murder and attempted murder by a jury at the Old Bailey.
Alan Newman QC, representing Inglis at the Court of Appeal in London, said: "She was entirely taken up with the belief that Tom was suffering and that he was trapped in a sort of living hell and in pain."
Mr Inglis suffered severe head injuries when he fell out of a moving ambulance in July 2007.
His mother first tried to end his life two months after the accident when he was being treated at Queens Hospital in Romford, Essex.
His heart stopped for six minutes but he was revived.
She was charged with attempted murder before successfully trying again in November 2008, after barricading herself in her son's room at the Gardens nursing home in Sawbridgeworth, Hertfordshire.
The hearing continues.