Murder

Watching as if through a glass.

Incomplete sentence here. You can get away with them sometimes, but it feels awkward for a first sentence. Who is watching?

I smile and am looked at with alarm.

If they're moving so slowly (which makes me thing they look kinda fuzzy) how can she tell?

It all floods back:

Kissing and pressing against Justin, finding a gun at my breast, Justin smiling and saying he was bored. Me feeling stunned and confused. I had run. He had shot.

"all floods back" is a bit trite. I think you can find some other way of saying it. Then the next part moves way too fast. First she feels the gun, then all of a sudden you tell us that she ran and he shot, basically all in one breath. Give us a little time to deal with each piece of info--describe the gun a little, maybe, then her running, and then the shot, instead of just telling us.

Now I’m here-watching the world fade away. Then there’s dark nothingness.

Nothing but nothing.

Tense switch, and a weirdly worded second sentence. Why not combine them, like so: "Now I'm here, watching the world fade away [incidentally, you could be a lot more descriptive here] into dark nothingness. "

The last sentence is redundantly redundant. You don't really need it.

Overall, this feels like a prologue as is, considering how short it is. You have the threads here. You need to stretch them out. Describe her standing wherever she is with this guy, describe what they're doing, describe how he says he's bored. Body language. Emotion. A bit more substance. Instead of writing in a few sentences what she remembers, show us it happening in a flashback.

Hope I helped! Let me know if you ever need anything.

Lupis

Watching as if through a glass. The world is moving slowly around me, doctors, friends, and family. They whisper to me but my ears hear only a soft buzzing.

If you're trying to convey that you're seeing things happen but not actually fully aware. might i suggest saying some thing like. seeing as if waking from a dream, i felt the world moving under me; slowly and sluggishly. I saw the faces of people i knew and didnt know. They were trying to speak to me.
friends, family, and...doctors? My ears were muffeled with the sound of buzzing
and instead of

I smile and am looked at with alarm.

:
I dreamilly smiled at them, i could make out the alarm and horror on thier faces. were they looking at me?

you should probably elaberate on being confused about why they were looking with alarm.

the part where justin murders you should be more discriptive. give the reader some thing to play with so they think they know what happened.

the last two parts are a good idea but worded awkwardly. hope i helped a bit.... Great idea!!!