Magic Sheep have deeper, darker meanings

I had a discussion with someone over on EQD about Luna's motivation and actions during Do Princesses Dream of Magic Sheep, and I realized that there was a much deeper, and somewhat morbid, interpretation of yesterday's episode.

Despite her veneer of being in control, Luna is a very emotional, very vulnerable soul. We've seen this in her before. During Luna Eclipsed when Twilight was approaching her at the Nightmare Moon statue, Luna looked very sad, lonely, and vulnerable, only to put on a mask as soon as she heard Twilight speak. We saw it again later in the same episode when she tried to make peace with Pinkie Pie. She was timid and hopeful when she held her hoof out.

In the opening scene of this episode, Luna tells the Tantabus "Do your worst", she is literally performing an act of self-harm. She created the Tantabus to punish her in perpetuity by forcing her to live her worst fears every single night! To me, this was eerily similar to someone cutting themselves.

The Tantabus became Luna's razor.

Let that sink in for a second. The Tantabus became Luna's razor, except instead of cutting her flesh she built it to cut into her soul.
She had created a semi-aware construct infused with her power over dreams to literally torment her every dream with how she became Nightmare Moon, her personal worst fear. In order to make it self-sustaining, she linked it's power with how much guilt she was feeling. This created a parallel to the "suicide spiral". She used her razor because she was feeling guilty, and using it just made her feel more guilt ridden than before. Because she could not bring herself to forgive her past, she empowered the Tantabus to punish her even more than before, goading it to new heights, cutting deeper and deeper. It became her crutch, how she was able to function in the world with the demons in her mind clawing around in the back of her head.

The Tantabus is Luna's razor.

The Tantabus, as I mentioned before, was semi-aware. As it grew in power it searched for better ways to perform its task, to punish Luna for her guilt using her greatest fears. Eventually, it locked onto her fear of dragging others down with her. It used its stored power to link with the Mane Six at first, and started using their fears to cause Luna even greater pain! It was able to constantly escape from Luna because subconsciously, Luna still felt guilty, therefore her creation continued about its task. Also, her insistence that she, and she alone must be the one to deal with it is very similar with how suicidal people feel that they are the only ones that are dealing with their problem and others cannot help them.
By the last part of the episode, Luna was unable to stop the Tantabus directly. Her friends, even knowing what it was and were doing their best to help, could only slow it down. They could prevent it from going further, but not get rid of it entirely. It was Luna's guilt, her fear, her unwillingness to forgive herself that empowered it to the point where is about about to enter Equestria proper. This is another parallel with suicidal behavior. Where was Celestia? In another parallel, family is often deliberately kept in the dark of a suicidal person's feelings. Luna didn't go to her sister because she was afraid of hurting her further.

The Tantabus was Luna's razor.

It wasn't until the very end of the episode, when Luna finally forgave herself did the Tantabus lose its power. When she stopped being afraid of herself, it lost its purpose. When she lost the desire to punish herself for her past, it lost its existence. But it was the counseling from Twilight that allowed her to do all of that, showing that there is a path to healing, if you are willing to let others help and get counseling.