My analysis is as follows
Tall buildings symbolize the position of body and mind in life, such as high position.
There are scenery and risks.
Falling from a tall building represents frustration, blow and failure.
You dream because you are uneasy about your environment and have a sense of crisis.
In addition, the change of life and the adjustment of work can all cause the dream of falling off a building.
Also, when sleeping, the external feeling of the body will also cause such dreams.
For example, take your feet off the bed.