You searched for: “somnambulist
somnambulist (s) (noun), somnambulists (pl)
Anyone who walks around while asleep: Just as the somnambulist reached the top of the stairs, his mother shrieked, and fortunately, he woke up before falling down the steps.
Word Entries at Get Words: “somnambulist
somnambulist
A sleepwalker.

"Just as the somnambulist reached the top of the stairs, his mother shrieked, and fortunately, he woke up."