It might sound strange, but I'll imagine going through with my method of choice... but not the aftermath. I might think fleetingly about someone discovering my body, or how gross it'll be to be a corpse. But I don't really think about the dead part. I mainly obsess over how I'll do it, and honestly try to avoid the part where my body goes into rigor mortis and/or shits itself.
I like to plan details like where I'll go, how I'll do it, what I'll need, what music I'll listen to, whether or not I'll send cliche final 'I love you' texts, etc.
I gloss over the being dead part because I think maybe I'll chicken out if I focus too much on my disgusting, decaying corpse.