Princess Luna, carrying out her normal duties of watching over the dreams of her subjects, comes across one of a more intimate variety. Normally unfazed by such dreams, this one embarrasses her into leaving quickly. Despite her decision to never think about the dream again—like always—she can't help but remember a single detail from it. A detail so strange she feels the need to talk to the dreamer about it. Unfortunately, she doesn't know who the dreamer was.
Awkwardness ensues.
For more story, read: One Day in the Life of Princess Celestia
For more awkward comedy (and story), read: Everypony Knows About the Wet Dream