You can start writing these fake scenarios and you will see that it doesn't make sense and then it should reduce.
No worry I am just like you as making stories of the future .now how I overcome this situation as I place the camera in the house so that when I do the work I immediately stop as someone is watching and trying to be busy and don't use the mobile phone too much as possible do this for 40 days then you are going to get a habit of that and you will slowly come to reality.
Can i know detaily what type of imaginary you are going through. Because i am also going through a imaginary, because of a hindi serial. I am always imagining about that serial even though that serial has went off air and it has been more than 3 to 4 years