One night after hours of working, Luna dozes off and gets visited by her worst nightmare: the thing that turned her into Nightmare Moon, to begin with, the Nightmare Force. "What? What do you want with me?" asks Luna.
"What else but for you to return to your Nightmare Moon form," responds the Nightmare Force. "You know you want to."
"No! Never!" responds Luna.
A few minutes later, Twilight stumbles by the sleeping princess and soon notices that she is shaking and flailing violently. Not knowing what else to do, she goes and grabs Celestia. The two then come running back to Luna's side.
"Luna, wake up," says Celestia as she shakes her sister. "Wake up. Why won't she wake up?" Celestia's eyes begin to well up with tears. She then turns to her last resort. She casts the dream walking spell on Luna and goes inside her mind. There, Celestia confronts the Nightmare Force.
"Why are you tormenting my sister? She doesn't deserve this!" yells Celestia madly.
"Because" responds the Nightmare Force, "it is time for the nightmare to rise again. "
"No, no it's not!" shouts Celestia at the Nightmare Force, tears in her eyes. "She will never feed into your darkness ever again." Luna then looks up at Celestia.
"Celestia, don't, don't anger it," says Luna weakly. "It will consume you. That's what it lives to do."
"Well," says Celestia turning to Luna, "I'm not letting it take you away from me again." Celestia then shoots a beam of light at the force and it vanishes, letting go of its hold on Luna and the two sisters leave the dream realm. Once out, Celestia tucks in Luna and lets her sleep for a little while. She then goes and raises the sun as it is now around 5:00 AM. They were struggling with the Nightmare Force for close to six hours, maybe more. All Celestia can hope for now is that the Nightmare Force will give up and leave Luna alone permanently. Alas, all she can do is hope.