The important facing questions are “where is my window facing” and “where is my bed facing in relation to the window and door”. Magnetism is irrelevant, as we are no migratory birds who can actually sense that field.
Although you’re practically right, we can technically actually sense magnetic fields. It’s incredibly weak and you have to drown out all other senses, but it’s possible.
Facing away from the door (I.e. having the door in the back) makes some people anxious, like people usually turn and face the door in an elevator. That’s why a hotel bed often faces the door.
The position relative to the window is a question of light.
situational awareness. humans instinctually need to feel safe. sleeping with your head right by the door gives you the least amount of reaction time/space to stave off invasion. inagine a rabbit sleeping with its nose out of a rabbit hole. in modern times with modern locks and security, its not a big consideration to be faie. but the instinct is there. people like headboards on beds for the same cavelike feelibg of protection. so yea head away from the door, bed not by the door. windows used to be avoided for being drafty or leaking light.