Mirror facing the bed
Old customs in Germany and Russia treated a mirror facing the bed with caution, and plenty of sleepers simply rest worse with one. At night the glass doubles every movement and light, and half-awake eyes mistake the image for company.
What it may mean
In daylight a mirror opposite the bed is just furniture. At night it becomes a second, darker room. Light from the street, a charging phone or a hallway lamp bounces off it, and when you turn over, a shape across the room turns too. In dim light the eye is very sensitive to movement at the edges of vision, so a sleepy brain may register your own image as someone in the room before it remembers what mirrors do. That small jolt can keep sleep light. Old customs in Germany and Russia treated mirrors at night with caution, and some covered them with cloth. You can take the custom as a question about rest. What in your bedroom keeps you on watch: a mirror, a screen, a pile of work in the corner? Beliefs about mirrors differ from culture to culture, and some people sleep soundly facing one.
Depending on how you saw it
Waking to a figure across the room
Waking at 3 a.m. and glimpsing a dark shape that moves when you move is startling, even after you realize it is you. The mind fills dim scenes with people. What else in your life looks like an intruder in the dark and turns out to be your own image?
A mirrored closet door opposite the bed
Mirrored wardrobe doors make a small room feel bigger and, at night, much busier. Some people hang a curtain or slide the doors to a plain panel. Which feature you chose for daytime does not suit your nights?
Covering the mirror before sleep
Draping a scarf or a cloth over a bedroom mirror is an old custom and a simple fix. The room goes still at once. What small covering could you add to your nights to help you stop keeping watch?
Moving the mirror and sleeping better
People who move a mirror often say they sleep better, though they are not sure why. Rest improves when the room asks nothing of you. What in your bedroom still asks something of you after dark?
Why it happens in nature
Mirrors bounce back any light in the room, so whoever lies in a bed facing one sees streetlight, screens and hall lamps twice. In dim light the eye relies on rod cells, which are good at catching movement at the edge of vision but poor at detail, so a moving image can startle you before you recognize it. Covering or moving the mirror removes both effects.
What folk beliefs say
Germany
In some parts of Germany, sleeping in a room where a mirror hung opposite the bed was thought to invite misfortune, so cautious people hung a piece of cloth over it.
Source: Cora Linn Daniels; C. M. Stevans (eds.), Encyclopaedia of Superstitions, Folklore, and the Occult Sciences of the World, vol. 1 (1903), vol. 1, p. 469. View the page
Russia
In Russia, people warned never to look in a looking-glass at night unless you wished to see the devil.
Source: Cora Linn Daniels; C. M. Stevans (eds.), Encyclopaedia of Superstitions, Folklore, and the Occult Sciences of the World, vol. 3 (1903), vol. 3, p. 1246. View the page
To reflect on
What in your bedroom keeps part of you on watch when you are trying to rest?