It does not seem that reliable. You have to plan it thoroughly, and even then, you might not be able to execute it perfectly.
I remember seeing this video of a Russian guy surviving a fall from a 19-story building:
Arguably, the guy was drunk and had no plan at all. But that just shows how inconsistent the approach can be if something goes wrong.
I heard that some people lose their consciousness even before hiting the ground, bcf heart attack in the air or something
Unless you start fainting before jumping, you will most likely not be able to lose consciousness before landing.
Let's take a 30-story building that is on the upper end of height. It should be around 350 feet tall on average. 350 feet is 107 meters.
The kinematic formula is S=a*(t^2)/2, where S is the distance traveled (107 meters), a is your gravitational acceleration (g=9.8 m/s^2), and t is the time it takes to land.
Solving for t yields t=sqrt(2*S/a)=sqrt(2*107/9.8)=4.7 seconds.
So, it is nearly impossible to do it that fast even if you drop from a high place. I guess it is most likely a myth.