in his/her sleep
Tom a dit que Mary était morte dans son sommeil.
Tom said Mary died in her sleep.
She talks in her sleep.
Elle est morte dans son sommeil, paisiblement.
She died peacefully in her sleep.
He died in his sleep.
Elle est morte paisiblement dans son sommeil.
She died peacefully in her sleep.
Sauf qu'après tu l'entends crier dans son sommeil.
Except then you hear him screaming in his sleep.
— Requiem pour un massacre (1985)
Tom parla dans son sommeil.
Tom talked in his sleep.