A thousand years is a very long time to be isolated and cut off from social interaction... Luna has shown remarkable coherency of mind since her return however. Her secret? She was never really alone on the moon.
After a shaky argument with Celestia sends her storming off to her chambers, old friends makes their return.
When you're a unicorn with immense magical powers, imaginary friends aren't quite as imaginary as one would think.
For best effect: Listen to this piece.

additional tags: short, v.random, silly. I just had.. to get this out of my head...

<Apologies, but after a minor nervous breakdown, I took down everything I'd written and hacked it all up with the writer equalient of a hacksaw, I'm slowly piecing it back together though, thank you for your patience.>

"Everypony in this town are CRAZY!"
- Twilight Sparkle

"Picture it: The chaos capital of the world."
- Discord

"Woof! Woof woof!"
- ??? (Screw Loose?)

Twilight Sparkle made a very keen observation upon arriving in the fair town of Ponyville. Which was also rather close to the truth. Almost everypony in Ponyville are crazy to some degree. It was intentional... Them being there, not them being crazy, that is. Though precautions had to be taken so one did not end up crazy as well. The town may have originally been settled by the Apple family to form part of Equestria's breadbask- er, applebasket, but its centralized location, safety and isolation from anywhere important meant it was also ideal to house the eccentric outbursts of its residents without bothering anypony. Several key members of Ponyville worked as doctors in addition to the "real" doctors. Gauging and checking up on the residents and ensuring they feel useful or simply providing some much needed social interaction... For the extreme cases Ponyville had a hospital facility with its own mental ward.

Occasionally strangers pass through town, unaware of its purpose. They tend not to stay long.

Sometimes they stay longer than they'd planned...