Dream experts will tell you that having dream where you are falling may symbolize that you are having a difficult time letting go of something in your waking like. In the case where falling in your dream feels good, then that is because you are deciding to let go of something you have been holding on to.
There is also the case where you are starting to fall asleep and you suddenly jerk, this is called a glitch. When we sleep our bodies become paralyzed so that we do not act out our dreams. hen we jerk it is because our minds scroll through images and we react before our bodies fully shut down for the night.