This is probably an episode from an American anthology show but I can't track it down. The wife's husband is killed (I think it's in a car crash) but is replaced by a doppelganger in the hospital. She knows it's not really him but nobody believes her. She has a young son. That's all I can remember.
This is the Hammer House of Horror episode, The Two Faces of Evil.
A hitch-hiker dressed in yellow oil skins attacks the driver of a car who has stopped to give him a lift. The car crashes and the driver fights with the insane hitch-hiker. It appears like the driver, though badly injured, has prevailed and is taken to hospital. The drivers wife subsequently learns that her husband has damaged his throat in the struggle and is unable to talk, she is also asked to identify the body of the madman. The body looks exactly like her husband and doubts begin to enter her mind as to which of the two is the killer.
If it's a straight thriller, and not horror/sci-fi, then a) this is the wrong forum, and b) it's been done several times. It might be :