Check your sarcasm detector it may be broken
It's hard when you start with a true statement.
they first thing that came to my mind when i saw the song title was The Fall as in the fall of Man (ie. Adam and Eve with Satan etc.), but then i remembered Opeth isn't religious at all pretty much. I also then looked at the lyrics, and it doesn't fit
Like I said in the past - and
philno loled at me for it - fall could be interpreted as falling, because that's somehow what happens to the protagonist when he discovers that "everything is lost", that "false love turned to pure hate"... he, the "wind", "cried a lamentation before merging with the grey". The protagonist's love "know it's [him]" and "keep the dagger close at hand" like if he had become something evil, that deserved hate (maybe because of his death), a demon.
And the most important part... "just one second and I was left with nothing" he lost her love and also his only reason to stay (run away is adressed to himself?).
To summarize the lyrics : There's a mournful and dreadful silence, she feels he - the protagonist - is near and she is suddenly scared and holds a dagger to defend from the presence, but then she sees nothing at all. Her love (which we learn, was not a sincere love) becomes hate toward him, like if she was persecuted, and the protagonist who's seeing the situation feels completly destroyed faced to a such hate. She screams out her rage and the protagonist decides that he must leave "in tears for all the eternity". Then all of a sudden she just face him, completly, and he feels like it's the time to run away, during that small span of time - just one second - he realised that her face showed that he had lost her and was left with nothing. He leaves forever (which is explained and detailed in Karma and in Epilogue, the final destiny).
Also notice that The Amen Corner informs us of something...
My breath in the sepulchral mound;
You know that your night is my day.
The final spark that blew life into me,
The demon of the fall.