I think that this song is from the perspective of a delusional person, possibly in psychosis, in a hospital. Aspects of the song including the "mice" may be a part of this person's hallucinations. The artist uses passive aggressive vocabulary such as "itching" and "gnaw" to enforce a seemingly eternal pain. The part near the centre of the song may represent the person's attempt at calming themselves down (we need to breathe, in such short spurts, inhale exhale inhale exhale). The majority of the rest of the song is about trying to make themself feel more secure and safe, but the paranoia is getting to him and he accepts his delusion that "They'll know I'm here, they'll gnaw right through". Something that particularly interests me is how the songwriter decides to use a vague "They" instead of accurately describing who "They" could actually be. It is up to us to interpret that how we wish. I would like to think that they could possibly be people from his past tormenting his mind in the present, although it is highly likely that "They" are yet another part of his delusions.