I think sometimes there are reasons and sometimes there is habit. I also think sometimes the mind is not as sensitive as the body. I'm thinking that because you say you were listening to music and I wonder if your body was triggered by something in the music beyond what your mind could comprehend? I know that may sound silly...I think if you get blind sided with urges you need to do your best to wait. At times like these it is the hardest because if you could understand why you felt like hurting yourself then you could do something to help yourself! I think the only thing you can do at those times is keep distracted and wait the wave of urges out. It is horrid, but I think the more you sit it out the next time it won't be as powerful....at least that's what I hope (and when I say 'next time', I don't really mean it is that easy but more 'in the future'!).