Chris Carter enjoyed the episode, saying "I really love that show. It's a great idea, well executed. We had a good cast; Tony Todd was wonderful" and saying it was "beautifully directed by Rob Bowman. "Entertainment Weekly" rated "Sleepless" with a B+, considering that Tony Todd's performance "elevates a just-good story into a great one." John Keegan Critical Myth gave the episode 7 out of 10, saying it was best remembered for its introduction of Alex Krycek. The web site further stated that the episode was decent and was a "fairly standard exploration" for the early season episodes. Dave Golder from "SFX" named the episode one of the "20 TV Sci-Fi Gamechangers" due to its introduction of Krycek.