It is definitely necessary to lean against the wall. Feng Shui emphasizes that the bed must have a backer. If you have no support, you will be restless at night and often dream.
Just like the placement of a desk, if your back is not against the wall but in an empty room, will you feel that there is always someone coming behind you, or that there is always someone coming behind you? If you feel something is wrong, it makes you mentally unstable and makes you feel uneasy when working or reading.
I don’t know the principle behind hanging crystals. The crystals themselves have radiation and magnetic fields.
The north-south direction of the bed complies with the penetration of the earth's magnetic field, which is helpful for the body. Do we need to hang a crystal to change the direction of the magnetic field?
If the bedside is by the window, you can Just put a few pots of plants on the windowsill, which has a feng shui effect.
If you are too noisy, close the windows to reduce the noise. The sound evil mentioned in Feng Shui also varies from person to person
Some people like to be noisy, so it cannot be called evil spirit. If you don't like it, you can call it Shengsha.
If you have any other Feng Shui questions, I would be happy to answer them for you