They depend on the situation really and no one can truly tell you if something is your past life or not as that is for you to determine. Often, people look into past lives for matters relevant to their current ones. Even if the dream wasn't your past life, the dream still could be used the same way to teach you a lesson relevant to you now (or perhaps later on down the road or even something to help you realize a matter in your past. It's all a growth process).
You could look into dream reentry. The technique comes from Aboriginal Dreamtime beliefs, but it can be adapted for your own paradigm. As I use it, it is a trance where one calls up their dream to delve further into it. Being that dreams are a bridge between the conscious and subconscious, as well as trance work, the practice fits quite well together in looking deeper into yourself and your spirituality.