Try DECAY or the really weird DEEP DARK (2015).
Believe me if you thought this film was weird and well done you will love DEEP DARK! Its very deep and very dark!
Its uncle Frank Kirsty!
Its time to play!
Soon, we will all have special names!

The first movie that came to mind when watching Excision was MAY (2002)
http://www.imdb.com/board/10303361/?ref_=fn_al_tt_1
but I just discovered this other movie titled KISSED (1996), that also seems similar.
http://www.imdb.com/board/10116783/?ref_=nv_sr_2

'Eat' is somewhat in the same genre. Maybe not as good as this one, but worth the watch!

May, American Mary, and a little bit of Donnie Darko

This reminded me a lot of Starry Eyes while I was watching it. Not for the subject matter so much as the tone, atmosphere, and the sense of building to something horrible and unstoppable, also for the incredibly stellar performances of both female leads. The brutality is comparable too.

Check out a movie called "Funny Games" for sureProbably one of the most horrific yet artistic, crazy movie I have ever seen

"Roman" (2006) is like a companion piece to "May".
I agree with "Sublime" (2007), and I'll third "Grace" (2009)
Others are:
The Skin I Live In (2011)
Victim (2010)
Danika (2006)
The Darkroom (2006)
Tideland (2005)
Trauma (2004)
The Nature of Nicholas (2002)
Otesanek aka Little Otik aka Greedy Guts (2000)
Boxing Helena (1993)
Buddy Boy (1991)
Alice aka Neco z Alenky (1988)
Possession (1981)
Repulsion (1965)
The Cabinet of Caligari (1962)~ Not quite in the same range, but I did find it interesting.
(W)hat are we without our dreams?
Making sure our fantasies
Do not overpower our realities. ~ RC

Dude, Definately check out STATIONS OF THE CROSS (2014) German film, it is very much like this!!!

Second Carrie (and remake).
Also would like to add Pretty Persuasion, which although is not horror, or bloody, has a similar feel to it when watching.
http://www.imdb.com/board/10381505/?ref_=nv_sr_1
If it's blood you're after, Long Pigs is about a cannibalistic serial killer;
http://www.imdb.com/board/10971204/?ref_=fn_al_tt_1
Those are your emotions acting without the benefit of intellect.

Didn't really think of it while watching it, but the original Carrie is similar to this movie. It's got the outcast weirdo girl, the antagonistic mom, and the mean high school kids. It's a little less grounded in reality, unless you believe in the existence of telekinetic people.

May (2002)

That
Excision
is mentioned in the same sentence is high praise indeed, and it deserves to be as well.
I'll second the recommendation for
Grace
.
The
Spike

You should check out "Grace" with Jordan Ladd.

I recommend that you check out Mientras duermes -
http://www.imdb.com/board/11437358/?ref_=sr_1
.
Whereas the plot is completely different, the atmosphere is rather similar. It's best watched without any prior knowledge of the plot - just be prepared for a dark and disturbing experience.

I'll second this. We Need to Talk About Kevin is so good too. It was originally a book, so it takes your fancy, you can totally nerd out on it some more. I think it has a similar vibe.
Plus, this list will be useful to you if you want to watch similar 'disturbing' flicks:
http://www.borrowingtape.com/top-200-most-disturbing-movies

I can recommend "We need to talk about Kevin".

Sublime comes to mind. Martyrs was 9000 times better than this, I would say.

Yeah may came to mind straight away. American Mary as the poster above suggested is also very good. French film martyrs is also very very good I definitely recommend that.

You should check out American Mary http://www.imdb.com/board/11959332/ Maybe not really the same but in the same vein.