Help with Short Horror Story

Im thinking of writing a short horror story over the summer holiday - as well with continuing my Dark Fantasy plan.

Im wanting to go with a kind of "Silent Hill" style horror where its about the contrast and also strange mix of two completly different worlds - normal world and some hellish (but usually all to real) world.

It will be in third person past but depending on the "world" the main char will be in (im thinking whether i will have only 1 character or not). For example, when hes in the "real/normal" world the "voice" of narration will be distant from the main character and will not focus on his feelings however, when hes in this hellish world the narration will be more personall and will focus alot on the character's feelings and thoughts - creating a bigger contrast.

I also want it to be set in 1 or 2 locals nothing more, hoping this will create a kind of claustraphobic but also more "personal" and "familier" feel even when the main character is in this "hellish" world which will still be in the same local as the normal world - search Silent Hill to understand.

I also want a percific action/object/or time which triggers the change between the worlds. I was thinking prehaps running water or a bath which is being filled would trigger the change - however if you have played Silent Hill 3 then this will be too un-original.

Well i really just thought of the idea a couple of hours ago and haven't done anything with it yet.

Please comment with ideas or help and ways of making it more "original".

-Thanks for your time.