Basically, it's about a person having nightmares or deliriae so intense, that they blend with reality.
A more in deep / detailed interpretation: this could be about a man telling the psychoanalyst ("faceless man in his chair, writing the diary of my life") about his nightmares and thinking, that this is a part of the nightmare itself. Then he realises, that this is real ("kill my dreams!").
Basically, it's about a person having nightmares or deliriae so intense, that they blend with reality.
A more in deep / detailed interpretation: this could be about a man telling the psychoanalyst ("faceless man in his chair, writing the diary of my life") about his nightmares and thinking, that this is a part of the nightmare itself. Then he realises, that this is real ("kill my dreams!").