Conversation so far:
What was Lou Reed's addiction?
Throughout the 1970s Reed was a heavy user of methamphetamine and alcohol.
When did he get over it?
From around 1979 Reed began to wean himself off drugs.
What happen next?
The Bells (1979) featured jazz trumpeter Don Cherry.
Around this period Reed also appeared as a sleazy record producer in Paul Simon's film One-Trick Pony.
Are there any other interesting aspects about this article?
Metal Machine Music (1975) was an hour of modulated feedback and guitar effects.
Critics interpreted it as a gesture of contempt.

Question: What was the commercial decline?
Self-contained rewrite: What was Lou Reed's commercial decline?