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Again I find it difficult to find any significant, much less abrupt, shift of tone(i.e. affect).
The stanza simply describes Shade's childhood fits, attacks, or seizures as a kind of enjoyable hallucination.
Sublime, although carrying connotations of nobility or purpose, is to be read mostly as a synonym for enjoyable, as in 2b & 3.
Shade isn't declining from something lofty in the first lines to something distinctly vulgar in the end.
It's all just one amorphous state. The particular metaphors, if that's right word to call them, also don't lead in that direction. Actually there's a progress from space-geography to time, to funnybone via tomorrow (future time).
And even if sublime connotes mystic oceanic feelings, there's no a priori reason for excluding the funnybone from those feelings.
There's a twist of sexual humor in the last line, set up by the previous line, but it just a slight comical stanza-ending flourish, and nothing substantial.