An interesting short, certainly a cut above most. Interesting comments too, it's unusual to see so many comments regarding the sound rather than just the cinematography, even if I don't fully agree with many of them!
I generally liked the cinematography, editing, pacing and the overall feel but the sound not so much. It's not that the sound was bad, just that it only achieved a fraction of what it could have achieved. What I mean by this is that the sound could have aided the story more and greatly improved the audience's feeling of involvement. The use of shot composition, angles and picture editing create visual implications and responses from the audience which we call the "language of film" and which you seem to understand and have employed well. However, there is also a "language of film" as far as the use of sound and music are concerned and you haven't employed this aspect of the "language of film" nearly as well.
It seems to me that visually you have used the language of film and told your story largely by contrasting/counterpointing real action as viewed from a third person perspective with cuts and flashbacks from the character's POV. For example, the character waking and sitting-up on the bed (third party POV) inter-cut with surreal images of the character's head pain and flashbacks from the character's POV, back to sitting on the bed, etc. The same happens in the balcony scene. Rather than enhancing this visual language and increasing the audience's involvement, your sound is frequently fighting your visual language and reducing the audience's involvement.
For example, in the language of film, music is great for creating mood but detracts from the realism/believability and audience involvement. Using non-diagetic music in film is by definition unreal/surreal and therefore always emphasises the fact that we are watching a film, rather than the opposite, which is making us (the audience) feel like we are there, sharing the experience with the character and forgetting that we are watching a film. This is what I mean by audience involvement. The cut to the balcony scene for instance still feels surreal and uninvolving, we have some isolated Foley sounds and the evolving synth pad to create mood but we have no atmosphere, no aural context. Is the balcony in a high-rise apartment block in the city or in a suburb or in the country? Without any type of atmosphere/believable audio environment, the audience cannot experience being "there" because there is no "there"! The same is true of the opening street scene and the bed scene, where the visual language says "real" but the sound says "unreal/surreal". Because of this, when we cut to a sequence which is supposed to feel surreal and/or inside the character's head, the impact is greatly reduced.
Prominent breathing sounds adds pace, energy and tension but also (in the language of film) implies first person perspective or at least intimacy/very close proximity. IMO, you've overused the breathing effects. In the opening scene for example the POV implication of the breathing is fighting the visual POV in places and creates too much energy/tension which lessens the contrast/dramatic impact of the subsequent shots/scene.
These might all seem like minor issues but they all add up to significantly reduce the power and impact of your short. Don't take this criticism too harshly, I've heard far, far worse use of sound and music. Your sound isn't bad but it's certainly not up to the same standards as other areas of your filmmaking. Just to be clear, it's not the technical quality I'm talking about, it's your artistic use of sound to create appropriate implications, manipulate the audience and aid your story telling.
I hope this is useful.
G