I think that is certainly a valid reading. But both can be true (especially since this can be read as embracing the madness). One of the cool things about the ending in my view is it can be read multiple ways. There have been times when I read it and your response has been what my response was. But the last few times I have read it, the character feels liberated and I tend to read the subtext as a person coming to terms with something like madness or a physical ailment, a condition that maybe has been inherited. Also just the way he paints the picture, whether our take away is meant to be horror or not, it just seems like he is painting a beautiful visual. And importantly, he doesn't seem anxious or upset like many of the characters at similar points in the telling of his stories. Personally I find the idea of living beneath the sea horrifying, as I don't like being in the ocean. And the bulk of the story reinforces that fear of the deep. But that last portion of the story surmounts that fear and embraces what life there might be. That it was written by a guy who seemed to be pretty fearful that he had inherited his parent's mental illness (and who may even have been feeling the first pangs of the physical illness the would eventual kill him----something I think you see traces of in the story), makes the alternate reading work for me. I do get it isn't a standard reading though.