I stand fairly certain that the DIY Brain Surgery page said NOTHING about hitting her in the chest with a hatchet...he very likely has a malpractice suit on his hands...
Seriously, though: this was a nice little "snapshot" short. The aesthetic was strong, and the ambiance was disturbing, and I think those were your two most major focuses. In that sense: bravo.
I do agree, however, that the psycho seemed a bit...overly psycho, and ThatGuyFromThatPlace absolutely hit the nail on the head as to why.
After watching it a few times, I think that it's specifically because of the moments at 1:10 and 2:07. These are the only two moments where he breaks away from his calm, almost sad persona that is established throughout the rest of the short, and it feels rather unprovoked. I think that in keeping with both the character and feel of the short, it might have been more disturbing if instead of looking at her crazily, he instead had a more subtle adoration in the glances he gave her. He could have possibly even made some gentle contact with her before slamming the hatchet down, like a hand on her cheek, or brushing a bang away from her face.
Just my opinion.