A short introspective story of how Luna came to be banished to the moon, and the aftermath of her return.
Fair warning, though, a quick skim or a casual read might leave one confused about what's going on. Conversely, I believe that taking your time to read and connect the details will answer any, or at least most, questions you might otherwise have.
And finally, any constructive feedback you might have is welcome, whether it's positive or negative. If there are issues that need to be fixed, it's better to know.
Picture used with kind permission from LifeSequenceBreak.
Chapters (1)
This was a very well written piece, and I enjoyed it more than a great deal of other fanfiction that I've read. The dialogue was compelling, and it was awesome to see Luna portrayed as regretful, but not a sad sack of tears. Your writing, technically, is very impressive, and even a little intimidating.
I have a couple of minor critiques, but I won't voice them unless you feel like hearing them - unsolicited criticism is always weird. Great story, keep on writing if they keep coming out like this!
1213
Like I said in the description, constructive criticism (especially when it comes to parts that need improvement) is welcome.
This was a great story, very touching.
I think the ending may have been a little weak, though. It felt a little unfinished. Besides that, it was a great story, keep up the great work! 
Hmmmm, it feels...rather disconnected. There were times throughout the story where I felt rather lost. Even with the summary to work with I was confused on what exactly was happening for the good first half. Most people should eventually realize it's a dream inside of a flashback/different scene, but it's still a bit of mess in terms of organization.
Also, the story, for me at least, reads as exposition. It doesn't feel like a story--the plot never really seems to move anywhere, it's more as if you're just setting something up to be expanded on later, rather than telling a tale.
I'd only give it a 2/5.
1532
I'm sorry you didn't like it; I know it would be hopelessly naive to expect that one's work would inherently appeal to everyone, but I still feel a little guilty about wasting anyone's time. That said, I'll try to clarify what I was aiming for.
Moving forward wasn't an intention when I set out to writing the story - or at least not a priority, and was intended to be more of a semi-historical, introspective piece instead. So rather than move forward, I decided to simply wind it back and play it to the beginning instead, and from there there wasn't much to go forward to - because once the reader realizes when it takes place, how the night ends is a foregone conclusion. Thus, I thought I'd focus on the "how", rather than the "what".
I also wanted to slowly draw the reader into the narrative, which I hope explains the confusion one might feel at first. I felt it would be more rewarding to paint the story piece by piece and let the reader assemble them into a complete picture, rather than deliver the entire exposition in one swoop. I also tried to do so with little parallels and callbacks between Luna's pre and post-banishment - some I think are subtle, others... less so. But I also felt it was just as important to leave some pieces out altogether and let the reader fill those in himself. For example, what did happen to Luna at the end? For that matter, what happened to her friend? That's for you to decide - if I wrote the story as well as I'd set out to, whatever you think will do better than any "...and then..." I could have followed it up with.
I hope that explains things a little and thanks again for reading,
Quinch
You're good, although, every now and then I get lost in the long mind rants, but it does add a nice look into her mind. If you want a bunch of negative feedback, I'm sorry I can't appease.
Good work, fellow writer.
1537
You don't have to feel guilty about anything; if you write a story, have fun writing it, and put honest effort into trying to make it good, then you've not wasted anyone's time. It's not like you forced anyone to read this or anything and you've seen people have enjoyed it.
Anyway, I'm not reviewer, so I can't say anything more than that I liked it. I thought some of the descriptions were a bit too much at times, but I like the way you wrote it and made a nice character piece that was sad Luna without her being just a crybaby or anything--by giving a solid example, you show just what it is she's feeling, and the reader can relate. It feels real to me, y'know?
This piece was good when I first read it, and it's still good now. Good piece.
I cannot believe it took me so long to come across this story, I enjoyed every part of this. The only disapointing part for me was it felt a little too short in some areas surrounding Luna's transition between her high and low moods. Otherwise, a remarkable read!
As a short story, Losing Ground is working with a strong premise, presuming I understand it well. Luna has a series of reflections about past events recent and long ago, and it is made apparent that the experience (and likely the mind) of Nightmare Moon is only repressed, not erased. Luna seems to leave Equestria after these series of reflections. Another strength of this story is that it has a mind for mood. Often using solemn or surreal imagery, I believe as a means to transition scenes, creates a dark and lonely mood, which builds up the credibility of Luna's thoughts and actions.
However effective the surreal is in establishing mood, in this instance, it takes away from the clarity of the story. Part of the reason for this is that the context for what is being shown takes a while to become established. Until late in the story, I was not confident in whether I was reading about events in the relative past or present. Clarity also can be an issue within scenes as well as the details in the material are occasionally dense and court purple prose.
Perhaps another matter to take into consideration is pacing. In the most simple terms, the plot is that Luna recalls a few scenes from the past, and at the point that recollection is done, she appears to leave for the moon. If Luna leaving is the climax of the story, there is a lot of room for building up to that in the relative present of the story to give that decision its due weight. As is, it seems that Luna comes to her decision very quickly, without indulging the notion that she as reformed as her sister believes. Were there to be more of a process or struggle leading up to her conclusion, building tension in the reader, it would charge the ending with a great dramatic energy. As is, I feel that the story creates more of a poetic sense of melancholy by the end.
Ultimately, I enjoyed reading this piece for successfully building that believable sense of melancholy and for challenging the notion that the Elements of Harmony just made everything magically okay through the power of weaponized friendship.