Huh, that's kind of wild. I'd assumed that blocking all light out at your eyes would do the same trick, I'll have to try the blackout curtains. Thanks!
I use a mask too, but it moves around when I sleep. Even properly positioned I haven’t found a mask that doesn’t leak around the edges.
I have this problem, too. I've tried probably a dozen masks, the best was one that I got overseas in Southeast Asia and it has no branding, etc.
Your face structure may be different than mine but I found this sleep mask stays put and works well at blocking out the light — https://www.amazon.com/gp/aw/d/B07D3M5TTZ