There’s a spooky, rundown house, and a visitor is in a first-floor room, and he realizes the stain on the ceiling - or is it even dripping down on him? - is because there’s a dead body in the room directly overhead. And that he is in imminent danger himself.
That’s all I remember. Ring a bell for anyone? Thanks!
Sounds like The Picture in the House.
The man who owns the house is a cannibal.
The very first Lovecraft story I ever read. And pretty atypical for him, because it’s actually a plausible and possible story, with no supernatural elements.
I recall reading that, but way back in high school. I am vague about the ending. Doesn’t something slightly bizarre occur in the final lines, like…
a bolt of lightning strikes the house, killing both men (even though one of them is narrating the story in the past tense)?
The text is in the link above - I interpreted it (rightly or wrongly) as:
Lightning coincidentally struck the house at that moment, knocking him unconscious and killing the old man. He speaks of his mind being saved, which is what led me to that interpretation.
The narrator definitely survives:
[spoiler]From the next to last paragraph: " The interruption was not produced by my fright, nor by the rapidly increasing storm amidst whose fury I was presently to open my eyes on a smoky solitude of blackened ruins."
Last line: “A moment later came the titanic thunderbolt of thunderbolts; blasting that accursed house of unutterable secrets and bringing the oblivion which alone saved my mind.”
So he was knocked unconscious and woke up to “a smoky solitude of blackened ruins”.[/spoiler]
There is a stain on the ceiling in Cool Air as well, but there is noone dead upstairs. More like undead. 
Thanks, everybody! That’s the one.