I envy you, Jos, not having to eat a pile of truly nauseating morning glory seeds for the experience.

Your account reminds me of Rimbaud's symbolist poem "Voyelles" (Vowels), found with its translation here:

Rimbaud, "Voyelles" translation

Rimbaud, of course, did a lot of psychological "experimentation."

Theophile Gautier, an influence on the Symbolists, was also interested in the poetics of synesthesia, writing a poem titled Symphonie en Blanc Majeur (Symphony in White Major), which itself does not otherwise employ synesthetic imagery.

Slight thread drift, but I wonder about the reverse influence, of synesthetic brain connections--natural or induced--on musical or poetic creativity.