So I think its interesting how I've looked through interpretations and no ones had this explanation...

To me, and I believe probably to Kurt, he saw the song as a metaphor to heroin. My girl was originally black girl, and kurt as we all know was deep into heroin around that time. Mexican heroin is referred to as "black" which is Seattle's main type. Then he goes on to say where did you sleep last night. In the pines sun dont ever shine I would shiver the whole night.

I think the song is mostly about not being able to score some black. The pines are the pins and needles you feel from withdrawal as well as the shivers and the sun never shines relates to how depressed you are during the comedown. As soon as I heard these lyrics I assumed it was about heroin. I used to be an addict myself so this speaks volumes to me.

P.s. dont know about the mans head. Maybe some horrible accident while high?