A warning dream is just what it says. These dreams often occur just after falling asleep. The message usually comes through loud and clear from the inner being, the soul part of us that wants to deliver the message. This choice, or this course of action, is not in your best long term interests. Such a message is couched in dream symbols that are usually so vivid that we wake almost immediately from the dream in an agitated state. Often fully aware, as if we have not been asleep at all. The memory of the dream and the symbols involved are so clear that, on waking, the participant has no choice than to face the message openly and honestly.
However, free choice is still a basic truth of the cosmos. So our choice to heed a warning dream, or ignore it, is still a choice we have to make with conscious awareness within our day-to-day reality.
Read about Precognative Dreams