I think I posted this a while back on this board, but I'm not sure. The following is a section of a paper at the lucidity institute. It explains levels of lucidity. A link to the full paper follows.

"We also showed that the tendency of nonlucid dreams to form transient global contexts is present during lucid dreams. Characters and situations encountered unintentionally in lucid dreams can serve as factors around which may nucleate a nonlucid dream context. These factors can compete with the lucid dream context for access to the dreamer’s intentions. If the lucid dreamer does not make a conscious effort to maintain the lucid dream context, it is possible for these distractions to absorb the attention of the lucid dreamer and draw the dreamer into a situation that unfolds independent of the dreamer’s volition. At the extreme, a newly generated dream context can displace the lucid dream context resulting in a loss of lucidity and the transformation of the lucid dream into a nonlucid dream. In practice, however, subtler forms of competition will allow the lucid dream context to co-exist with competing dream elements that are not contained in the lucid dream context, resulting in modifications of the cognition of the lucid dreamer which affect memory access, thinking and behavior. In such situations, the dreamer appears to phase in and out of lucidity to various degrees. Thus, because of competitive processes, the degree of lucidity can itself vary within a single lucid dream. "

http://www.lucidity.com/VOLDE.html