When you were young, you had a dream about falling down into a ravine. years later you are mistakenly convinced that as a child you fell into a ravine. this is best explained by

This can be explained by Source Monitoring Error. This is a memory error and occurs when we attribute a memory to a wrong source or situation. In this case, the memory of what is dreamed is mistakenly attributed to a situation actually experienced. This memory error is very common and it often happens from childhood memories.