Everyone's bottom is different. What it took for one person to recover may be very different from the next person sitting next to him in a meeting. For some people I know, it was not until they were homeless after getting out of jail for an alcohol-related crime that they could begin their recovery. For me, it was the realization that for all of my adult life, I hadn't started or ended any romantic relationship without alcohol -- often alcohol was involved in both the beginning and the end. It took a different kind of relationship for me to see the big picture and realize my life would never be any different unless I changed my drinking.
At first I held onto the idea that I would somehow one day be able to drink like a normal person. The more I learned about alcoholism, though, the clearer the picture became -- I'm simply not capable of doing that. When the genetic lottery was handed out, I got a lot of good things and a few things that sucked -- and my reaction to alcohol is one of the things that I wish were different.
It took half a lifetime of denial before I could even think about letting go of drinking. "Bottom" didn't come when I woke up passed out on the floor in my own vomit, with blood in it from how sick I had been. "Bottom" didn't come after the day I performed a public strip show for people I had just met and later had unprotected sex with at least two of them. "Bottom" didn't come when I needed stitches in my leg and didn't get them because I was too wasted to know I needed medical attention. "Bottom" didn't come in any of the incredibly hurtful moments that happened in my relationships because of my drinking. I just had to be ready.
I could have kept going for a while longer before I faced any real consequences outside of my social life, which I just kept rearranging around my alcohol-induced mistakes. But how much longer until I lost my job due to poor performance, had an accident or got arrested for a DUI, sustained a really serious injury from being drunk... I think if I had kept on the path I was on, despite my belief that I was untouchable because none of it had happened yet -- I would have wound up with some or all of those events in my life.
So, how do you know? You don't until later, when you've got some recovery time under your belt and a clearer head. Then you can look back and say yes, this was bottom for me. There's no sense to go pounding on it looking for the trapdoor that LaFemme mentioned; you'll find a way down to a deeper level of trouble if you want that.