First of all, you should sleep in a position with the head of the bed against a solid wall. Your head should be opposite the door so that you can see the door. Don't sleep with a space behind your head. If you are sleeping with your head toward a window, change it, or at least put a headboard on your bed. You shouldn't have your head against mirrors as they are reflective and bounce energy. They will disturb your energy field so that you can't sleep. It is usually good to put the head of the bed in the far corner of the room from the door with your head against a wall.
You should never sleep right in line with the doorway, there is too much energy coming through the door and you can't relax, and it will cause problems to your peace of mind. You also don't want to sleep with your head to a wall that has plumbing in it, or a wall with a computer, television or refrigerator on the other side, because these all have large electromagnetic fields. You want to sleep with your head against a wall that is nice and quiet.
Try not to position your bed under the lower angle of a pitched ceiling, a ceiling fan or a heavy beam. These features are thought to contain "depressing energy" that literally pushes down on you while you sleep. If you have no choice, a bed canopy or lengths of fabric suspended from the ceiling or beams are believed to be Feng Shui "cures" for the problem. If possible, position the bed away from overhead beams. Heavy beams create pressure over the area directly beneath them. This pressure is called Sha Chi and can cause health problems. For example, if a beam is directly over your head at night you might suffer from headaches; over the knees and feet can create knee and leg problems; over the stomach can cause digestive problems; and beams running lengthwise over the bed can cause relationship problems (since it's separating the couple). The lower the ceiling the greater the impact.
Clear out everything under your bed, as the chi of things underneath you will affect you all night long and will block energy and lead to stagnation in life. Having back problems or trouble sleeping? Don't blame the mattress necessarily. The type of objects you keep under the bed can affect your sleep and health. When your bedroom is cluttered and untidy, the energy in there will be low and slow.