Why do you dream that your falling and it feels real?

The sensation of falling as you fall asleep is known as hypnagogic myoclonic twitch or "Hypnic jerk".

Most experts agree that this is a natural part of the sleeping process, much like slower breathing and a reduced heartbeat. The occurance is well known and has been well documented. However, experts are still not completely sure why the body does this.

There are some theories as to why this happens:

"One is that hypnic jerks are a natural step in the body's transition from alertness to sleep. As you drift off, your body goes through some physiological changes to prepare for a few hours of restoration. Your breathing rate changes. Your temperature may change. And your muscle tone changes, too. Hypnic jerks, the theory goes, may just be a byproduct of that muscular transition."

"Second theory says that, as you slide toward sleep, there's a point at which your muscles really let go. Your brain, which after all did evolve from a reptile brain, interprets this rush of relaxation data as a sure sign that you're falling down. And it tells your arms and legs to thrash around and keep you upright"