Yes, I think it's "thank you, drop dead" as well.
The paradoxical thing is that anti-depressants and anxiolytics tend to quash the libido. Sometimes the depression and anxiety itself dampens the libido already. I've always thought Moz was talking about impotence and the way depression can just blot out physical desire/pleasure in this couplet:
"And Sorrow's native son
He will not rise/smile for anyone"
Then again, lithium is used mainly as a mood stabiliser for manic depressives. If in a manic phase, the speaker might be, uh, feeling excessively frisky.
Someone else I talked to thought he heard "BITE ME". How rude, Mozza!