"Highly functioning" and "heavy drinker" are oxymorons. What you think is high functioning is not even in the realm of what a person that doesn't drink considers high functioning. You can't see that when you are in the midst of the addiction, but there is no such thing as "high functioning" when you are a drunk. Every aspect of your life is being held back by alcohol, when you drink enough, it pervades everything. I used to describe myself as "high functioning" during most of my drinking days, but that thought process was pure addictive voice convincing me that the way I drank was not a big deal. Looking back, I see that the way I drank and lived was utter lunacy.
The good news is there is a whole 'nother world out there that is available to you if you stop drinking. It's not a world I knew about or understood when I was an active drunk. It's full of hope and possibilities. It's freedom.
Welcome aboard, you can do this. You have to want it, but it can be done.