My 4 year old won't go to bed!

[MELIAMY1992]

So my 4 year old has always been brilliant going to bed, story kiss & cuddle lights out. Over the last week he just wont go to sleep until we do every night has been a battle he wants us upstairs with him and gets very upset.
Even during day time he gets upset if he can't see me or if he goes in the garden the door has to be wide open even if I'm in the kitchen watching him. He has to reassured numerous times of the day where I am. Please has anyone got advice because I'm losing my mind

What's happend to make him react like this? Has there been a sudden change where you weren't with him when he expected you to be? Even just a bit late picking him up from school. What's he said when you've asked why he's suddenly upset about this?

I've tried thinking to myself what may of triggered it, it could be that I'm working an extra day, I went away for one night with work but with plenty of warning and explain I'll see him the next day. Everytime I ask the answer is so off subject. Even when I try and put him back to bed he's screams in his bed which is waking his sister she's losing alot of sleep over this too. He become very obsessed about closed doors he wants to know if the living room door is open whilst we are downstairs whilst he's in bed. I really am struggling especially during the working week and being a teacher myself going from working with children to come home and minimal sleep I'm on my knees!