nocturnal death syndrome sounds nice to me. i imagine myself closing my eyes and settling in for the night, dreaming -- then, without any pain or panic, the flow of consciousness permanently halts, and i'm gone. it's the cleanest, closest thing to snapping my fingers and no longer existing, all wrapped up in a dream.
it would be a pretty horrible way to go if you had something to look forward to, or if you value agency in your exit (which is completely understandable!), but it doesn't really matter to me.