The south corner is considered as a direction of Death. It also said that the Yamalok ( hell ) is located in the south of the universe and beneath the earth.
Normally when a person dies, his/her body should be kept in a position like head towards north. This is one of the strong reason that people avoid sleeping head towards north direction. For more information read Narak article from Wikipedia.
Science says that it is because the human body has its own magnetic field (Also known as hearts magnetic field, because of the flow of blood) and Earth is a giant magnet.
When we sleep with head towards north, our body's magnetic field becomes completely asymmetrical to the Earth's Magnetic field.
That cause problems related to blood pressure and our heart needs to work harder in order to overcome this asymmetry of Magnetic fields. Apart from this, another reason is that our body has significant amount of iron in our blood.
When we sleep in this position, iron from the whole body starts to congregate in our brain which can cause a headache, Alzheimer’s Disease, Cognitive Decline, Parkinson disease and brain degeneration. All these things don't happen in one or two single night but it happens if the person has a daily habit of sleeping in a north direction.
