BEWARE: You May Suffer From Sleep-Drunkenness. “Ohayon explains that while researchers aren’t exactly sure what causes this confused behavior, animal studies give us a clue: Sudden awakenings seem to trigger the startle reflex, which allows animals (and, likely, us) to respond quickly to potential threats. To our poor, half-asleep brains, an abrupt awakening signals an emergency — a time for action, not reason. This is also, incidentally, a reason to reconsider your hilarious idea to wake up your sleeping buddy while wearing a terrifying mask; judging from the (slightly NSFW) evidence on YouTube, sleep-drunk individuals are likely to respond to the prank by punching you in the face.”

Seems fair.