He is 5.5 and he's always been quite sensitive and thinks about things a lot. About a week ago he watched an episode of Bottle Top Bill where there was a mummy at a museum, and DS didn't it. Since then every time he goes to bed he gets upset and says he can't stop thinking about it. Its not a nightmare when he's asleep, its before he goes to sleep. We've tried talking it through with him, but he doesn't really want to talk about it. We sit with him and talk about other funny things to try to take his mind of it and we've left a night light on for him and his door open, but he still says he can't get it out of his head.
He seems to be getting progressively more upset each night - last night he kept shouting us and we heard him sobbing to himself in bed. DP went up and DS was virtually begging him to erase the thoughts from his memory and got really upset when DP said he couldn't do that! So he suggested putting his lamp on and reading a book until he was so tired he'd fall asleep. At 10pm I went up to bed and he was still reading his book - he said he couldn't stop because then the scary thoughts would come back into his head 
This morning he was really tired because he's obviously not had enough sleep. Any ideas of what we can try. We've now all started to dread bedtimes!