A spokesman at St Bernard's Hospital said no further information about his condition or its cause was available.
However, the Attorney General's office in Gibraltar said Mr Newall appeared to have taken a drugs overdose. Prison authorities meanwhile said his life was out of danger.
Mr Newall has been taking medication while in custody, and his lawyer has complained on his behalf about conditions in prison.
Three months ago Mr Newall, 27, tried to commit suicide by slashing his wrists and groin.
Police in Gibraltar have held Mr Newall in custody since his arrest at sea in August, when his yacht, Austral Soma, was stopped by a Royal Navy frigate off the north African coast.
Mr Newall is fighting extradition proceedings to return him to Jersey to face trial.
His parents, Nicholas and Elizabeth, disappeared in October 1987 after a celebration meal at the Sea Crest Hotel, St Brelade, Jersey.
Their bodies have never been found.Reuse content