For many people, this is the most common cause of falling down (atleast in their dreams). Losing balance, and consequently falling down could mean there may be an incongruence, non-compatibility or misbalance in your life which you are struggling to correct.
There could be multiple reasons for this imbalance to occur- going through a financial crisis, bad work-life balance, struggling to settle, hanging onto something from the past. All of these factors can weigh down heavily in your mind and affect you subconsciously, making you prone to having dreams about falling.
If you slip and fall out of the blue, it can be taken as a sign of emotional trouble, a slippery, risky situation you might be navigating in your personal life.