Human eyes have motion detectors. Our eyeballs are naturally attracted in the direction of movement
If you have a mirror facing your bed, and you see the reflection of any moving object in the mirror, your eyes will instantly focus in the direction of motion. And it will distract your sleep.
Some people experience a condition known as “Sleep drunkenness”. In this condition, their visual senses are not fully awake right after they wake up.
They can scare themselves by looking accidentally in the mirror right after they wake up.
Commonly domestic mirrors are not “perfect mirrors”. These mirrors show some green reflections that might creep you. It is not a supernatural phenomenon
You might notice louder sounds if you sleep near the closet mirror than you sleep anywhere else. If your partner snores and you hear a louder reflected snoring sound, it may affect your sleep quality.