nightmares

[jo-ane]

my 9 year old son has just starting having nightmares and it is the same every night, he thinks someone will break into our house and he is murdered, it is really upsetting him and getting him into bed has become a real battle. It is also making him very tired during the day as he is keeping himself awake as long as he can. What can I do I have tried to reassure him but nothing is working, why has this just started?