The reason why you should not sleep with a mirror in front of your bed is because it can result in nightmares and insomnia.
The belief is that the mirror in front of your bed bounces energy and doubles it, which virtually interrupts the peacefulness within your bedroom.
A half mirror is a reciprocal mirror which appears reflective from one side and transparent from the other side.
A half mirror is also known as a one way mirror which has a thin reflective coating called a half silvered surface and the surface makes the glass translucent and only reflect about half the light that strikes it's surface.
When you point two mirrors at each other or put a mirror in front of a mirror an infinite virtual image will be created which is an image you cannot touch.
The same image is basically flipped as it would be in a flat/plane mirror and for an infinite number of times while getting smaller each time.
Mirrors facing each other create what's known as an "infinity mirror" effect.
The infinity mirror effect is a series of reflections that appear to go on forever.
It can be super trippy to look at and a cool trick of optics, but it's not a gateway to the netherworld.
When you have two mirrors across from each other, they are streaming energy back and forth between them.
This is definitely something you do not want if they are placed in an area that you sit or sleep between.
This is way too much energy for a relaxing or peaceful space.
If you place two mirrors facing each other in a dark room, legend says you have created a ghost portal through which spirits can pass.