My 10 year old suddenly stopped going to sleep

[JosieJo2212]

Any help or advice greatfully received.
For the past 3-4 weeks my son who has always gone to bed at 8.30pm and slept right the way through has started to get anxious and refuses to got to sleep. He can often still be awake at midnight or even as far as 2am.
He has a calm pre-bed routine, reads in bed no computer games, no tv, no sweet or caffine drinks.
He says nothing is worrying him except that he thinks I'm going to leave him. This is ridiculous as there is no evidence for him to think this. My relationship is fine, there are no rows in the house, i don't go out socialising, there is nothing to give him any impression that I am leaving him or going out of the house. Its as if he's developed this major anxiety complex from out of nowhere. he also says all is fine at school and I have no reason to disbelieve him
Does anyone have any suggestions?

I'd take him to gp if you can't think of anything that has triggered this fear.

I used to refuse to sleep as a child because of terrible nightmares - even a one off one can have a bad reaction.

Does he listen to audiobooks at night because that can help (giving them something else to concentrate on).