It's gonna be one of those days, isn't it? · 2:01am Feb 11th, 2013
I'm too lazy right now to write out something lengthy, so I'll get to the point as soon as possible.
Greetings readers.
For the past month or so I feel as if I have been "losing my touch" when it comes to writing. I can barely write fluently anymore, let alone at the usual level of quality. I've been stressing out over this for, quite literally, months on end. There hasn't been a single day of my life so far where I did anything but worry about my writing. It's frustrating the hell out of me and, most of the time, forces me to get little sleep just because of my continued struggles in the areas of how a paragraph looks/sounds. Every word, every sentence, and every paragraph feels like a great big frustrating chore to me.
And I'm fucking sick of it.
Let me show you an example.
"She lifted her head and opened her already-closed eyes in readiness to peer into the unknown. Standing across from her only a few feet away was the very recognizable figure of a pony, a very tall pony at that, whose body shape resembled that of a grown mare. Her mind went straight to the image of an alicorn, immediately thinking of the three princesses in the royal cities of Equestria, but the thought was quickly rejected once she saw that the pony lacked the hefty, trademark wings of the regal species. It did however possess a long, white horn matching its shiny coat color. Its mane and tail were just as remarkable. Unlike the princesses, they did not flow like they were caught in the grip of an invisible breeze, but their luxurious colors of emerald and navy blue were two things that could give Celestia’s mane a run for its money. Its eyes were without a doubt the most dazzling part of its body, for they too were of a deep blue in color and sparkled like gemstones. Everything about the mare resembled magnificence in its prime, but what was she doing here, and why?"
See this paragraph right here?
It took me two days to write this fucker.
Two days.
For a single paragraph.
In my world, that is execrable in the name of progress. I'm losing my grip on what I think is considered quality writing and what isn't. What do you guys think? Does this paragraph provide a good example of whether or not my quality of writing is going off the rails? Am I doing too much or too little?
Also, spoilers. 
-Hivemind 
Quality is based on the way your perceive your work.
On our part, we may see it as something brilliant.
In the eyes of a poet lies his art, and in those of an author his. I believe that, whatever hindrances may be there, if you believe that you have a quality product in the end, and so do your readers, who is there to say that your writing is not of quality? For if I am to sit beneath my roof and write my poetry, great or small, rhyme or prose, and all that see it call it good, but I am not satisfied with it, then who is to say that it is not terrible? Your art is yours, and whatever that be, it is in your eyes that it must gleam.
I'm done being pretentious now. Do you feel what I'm sayin' here, though?
If your really feeling stressed out remember the sloth. They don't do shit and they haven't gone extinct. I think you can afford to take a nap.
You need to take a break is what it sounds like. You stress about writing is killing your writing. Your writing is stopping your writing. You might need to end that process and breath a little. Focus somewhere else. Let anything recursive be forgotten. Clear your mind.
If there's one thing I've learned over my course of time on this website, it's that if you get that burden-like feeling, step away from it. Take some time off, clear your head, don't put too much stock into your writing. We all need a break every now and then and there's no harm in taking one.
Since you asked, allow my humble critique...
From that short example, the only problem I see is that you appear to be using overly complicated sentence structure, without any reason for it. For example: "She lifted her head and opened her already-closed eyes in readiness to peer into the unknown." Did she open her eyes in readiness or lift her head in readiness, or both? If she opened her eyes now (in the paragraph), why do we need to know they were closed, presumably in the previous sentence? If her eyes being closed were important, we would still remember it from the previous paragraph, no need to reiterate. If not important, why mention it in the first place?
Simplify. Write short, precise sentences and the make them more complicated as necessary.
Simple: "She lifted her head and opened her eyes wide. She was prepared to look into the unknown."
Embellish: "She raised her head and focused her eyes, primed to peer into the unknown."
The content is fine. I think a little simplification would go a long way to help your struggles to write things you will be proud of. Also, don't forget to write out the whole thing quickly first, THEN edit (and get initial critiques).