The weight of the head is supported by the Cervical Spine.
The cervical spine in the body is what supports the weight of the bodies head and neck.
The human cervical spine is the most superior portion of the vertebral column and the cervical spine lies between the cranium and the thoracic vertebrae.
Without the cervical spine the head and neck could not be supported properly.
The cervical spines job is to also allow the motion of our heads and neck so it has more than one job in the body and is very important.
The bodies neck can support the average humans weight as long as they are not too heavy.
However the neck cannot support your body weight if it the neck has some rope tied around it and you're suddenly dropped.
Even if a rope was around your neck and you were dropped down slowly you would still eventually die due to asphyxiation and your neck will likely eventually snap due to the bodies weight.
However if you were to stand upside down on your head and had someone hold your legs up in the air then your head and neck could support the weight for a short while.
An average human head weighs between 10 to 11 lbs for an adult head and around 1 lb for an infant and 2 to 3 lbs for a 1 year old to 3 year old.