I tried mouth tape and woke up with it off — does that mean it's not working?

Not necessarily. There are a few common reasons tape comes off: (1) skin was oily or had product on it at application, (2) the adhesive wasn't strong enough for your skin type, (3) you naturally opened your mouth wide enough to break the seal. Try applying to clean, dry skin and pressing firmly for 5 seconds. If it still comes off, you may need a tape with stronger adhesive or a wider coverage design. Some people also find that after 3-5 nights of consistent taping, their jaw muscles "learn" to stay closed and the tape comes off less. Your body adapts.