[9] According to Loudwire's Sarai C., "Sleepwalking" begins "with an electronic melody which evolves into a powerful minor chord progression, paired with Sykes' perfectly executed vocals", and also features some nu metal influence.

[13] Directed by A Nice Idea Every Day and Richard Sidwell,[14] it depicts a sleepwalker "[traversing] wintery landscapes and a seagull-infested dock whilst in the land of nod", while Bring Me the Horizon "perform the somnambulist-inspired tune for a bunch of depressed pint-sippers in a pub".

[15] BBC Music's Mike Diver proposed that "Sleepwalking" and opening track "Can You Feel My Heart" introduce "new, synthetic textures to the forefront of" the band's sound.

[16] Reviewing Sempiternal for PopMatters, Dean Brown praised the addition of Jordan Fish's keyboards to the band's sound, particularly on "Sleepwalking" and "And the Snakes Start to Sing", which he claimed "splash[ed] colour" onto the songs' "sparse sections".

Writer Dan Slessor claimed that it features "perhaps the most rousing chorus in [the band's] catalog, a stuttering breakdown ... a sublime bridge ... [and a] gigantic climax".

[18] AXS also included the song at number five on its list of the band's best tracks,[7] while Metal Hammer writer Luke Morton ranked it the seventh best, praising its accessible and anthemic nature.