Can be divided into three types:
1, subconscious sorting and archiving of memory (memory)
2, the body is not timely subconscious warning (body warning)
3. The result (prediction) inferred by subconscious mind according to memory and thinking logic.
If your dream is accidental, it should be the second kind, probably because the blood in your legs is not smooth and you are numb when you sleep. The scene given by your subconscious mind is that your leg is gone; If this dream appears many times in a row, it is likely that there are some problems in your leg that have not been discovered for the time being.