“Sleep Walk” is pretty famous for its I – vi – iv – V verses, but there’s more interesting stuff going on, especially for 1959 top 40 radio.

• The end of the bridge is a G7#9 (AKA the “Purple Haze” chord). The slide emphasizes this by sliding [D, G] up to [F, Bb] and back, and you can really hear the [B, F, Bb] in the rhythm guitar. I can’t think of any other top 40 song that used it so prominently; even “Purple Haze” mostly omits the major 3rd so it’s not as dissonant.
• The ending is a G chord with the slide using a falling sixth interval: [G, E] – [Gb, Eb] – [F, D]. This is a common blues trick that turns a 6th chord (6 on top) into a 7th (7 on bottom).
• The final cadence is pure jazz:
  • C6 [8-x-7-9-8-x]
  • G7b9+ [x-8-9-8-9-x] (root played only by bass)
  • C6add9 [x-10-10-9-10-10]