When someone suddenly collapses, this may be due to a number of problems. It may be due to internal or external bleeding, hypoglycaemia (low blood sugar level), cardiac arrest, heart failure etc.
Whatever it is, such person needs urgent medical attention. He or she should be taken to the hospital as fast as possible for the condition (leading to the collapse) to be diagnosed and managed accordingly.
Someone who just collapses should be made to lie flat and transported to the hospital that way.
This allows the heart to supply blood to vital parts of the body without the influence of the force of gravity, especially if the collapse is due to blood loss (external, internal or both) or is related to heart failure.
For those with cardiac arrest, extra efforts at cardiopulmonary resuscitation (CPR) should be made to keep the person alive while being taken to the hospital.
It is unfortunate that sometimes, people try to either sit the person, who just collapses, up or even stand the person on his feet to assure them he or she is still alive.
It is important to know that this is against the survival of the individual, as gravity will pull whatever blood remains in the person down to the lower part of the body which is less important for the survival of the individual at that particular time, depriving the vital organs of the body necessary blood supply needed for survival.