In the beginning, it is normal to wake up and occasionally find that you’ve removed the mouthpiece. It’s also normal to temporarily break the seal occasionally during the night when you swallow or move around. The seal will typically re-establish on its own.
If you frequently have trouble keeping the mouthpiece in at night or keeping your mouth closed while sleeping, you might find a chin strap helpful. Other options include using mouth tape or facial tape. Speaking with your doctor can also be helpful and result in additional recommendations.