wait
How could you have read this thousands of times already
Normal thing becomes scary thing, scary thing chases protagonist, protagonist hides in house, scary thing kills protagonist.
This is actually a regularly used formula.
The imagination thing makes it even more silly, because if the protagonist acknowledges it's not real, then the only thing that kills him is himself. Which then makes this Self Delete. Which then just makes this a messed up Self Delete note. Which is another trite formula.