Do you feel like you're in over your head? Maybe you're caving under the pressure of a certain task or duty. These anxious feelings will most likely result in a dream of you falling or drowning. Dreams revolving around a continuous fall or drowning demonstrate an internalized anxiety about a situation or task at hand. The emotions they evoke can range from loss of control to exhilaration. Your specific reaction in this nightmare will likely mirror your reaction to certain circumstances in reality.
This is also a perfect opportunity to engage in lucid dreaming. If you know you have this dream often, you can resolve these falling and drowning anxieties by realizing it's all a dream, and then willing yourself to control it. Instead of falling or drowning, tell yourself to fly or swim. After all, it is your dream, and within it you can do whatever you please.