Can anyone tell me why an article is left out before the expression "rock bottom" despite the word "bottom" being a countable noun? For example:
My sport career has fallen down to rock bottom.
Would it not be better to insert the article a?
I believe it is just an idiomatic usage.
Also, we usually hit rock bottom:
After that, my career hit rock bottom.
Taking a more literal approach, you could look at bottom, but
I was at the bottom of the river of my life.
but then the article is back. So I don't believe a literal explanation will suffice.