Question

How can your body replicate the feeling of falling from a high altitude in a nightmare if u have never fallen before ?​

Answer 1

Answer:

It doesn't. That feeling is what you feel when you trip and fall. It's the change in velocity and the instinctive attempt to correct.

Actually falling from high altitudes doesn't feel anything like that panicked breathless fluttering people get while falling in a dream. At least, not after the first few seconds.