Sleeping with your mouth taped shut may sound extreme, but that’s become a viral “sleep hack” on TikTok and Instagram. Influencers call it a fix for snoring, bad breath, and even jawline definition.

Everywhere I've been, it's been the same: Entering mysterious worlds through kitchens or bedrooms or offices or hallways. No matter where I go, I put on the headset, draw the magical boundaries of my ...