Well, most of us go through a stage where we have far too much to drink, sometimes more than once, maybe have no recollection what we did for an hour or so, and spend the next day vomiting and regretting it, then end up doing it again a few months later. Most of us grow out of that pattern of behaviour - it is very juvenile.
It's quite another thing to be losing hours and hours from your memory and waking up injured in hospital with property missing. That's fairly extreme really, and when I see that happening on documentaries I certainly don't go all nostalgic and think "aaah, poor lad, we've all been there". I just think "Jesus Christ, how awful to get in that state". Very occasionally it's obvious that it's a one off and the person is horrified and ashamed, but usually it's clear it's not the first time they've ended up like that and won't be the last. I guess you just don't know yet which camp they fall into.
I will say, though, that I know someone who has had a horrible relationship with alcohol since he started drinking in his youth (mid teens, he had older brothers and just joined in with how they were behaving I think). He also got a reputation amongst his friends for going over the top with drinking, like your DC, OP. So many photos of him just in a state at parties when everyone else is just "normal drunk" and smiling at the camera.
He's past the age of 40 now and over the years it has caused multiple problems in relationships, both with partners and the wider family. Even when he was done for drink driving (he claims he wasn't actually driving, just sitting in his car listening to music with someone 
) he didn't moderate his behaviour. He ended up falling down the stairs drunk at a party and taken to the same A&E dept where he worked. The irony. Can't imagine the shame. And despite the fact that he could have quite easily killed himself and left his 2 kids without a dad, still it carried on, I believe, and he ended up getting divorced from his wife (was blame on both sides, it wasn't just because of the drinking).
I THINK he has just grown out of it a bit now, but god, he's mid 40s so he's spent a lot of his adulthood nearly killing himself or causing issues for others.
What I'm trying to say is that even though he dealt with drunks in A&E himself, it didn't stop him ending up as one himself. If a person has a problem with alcohol then they have a problem they can't control, and they don't think of how their behaviour impacts on others. They just want to drink what they want and act how they want. Unless someone pulls them up on it, they're just going to carry on like that. The person I know and his brothers ALL had a problem relationship with alcohol over the years, and I do believe that it's because their parents had a "boys will be boys" type of eye roll kind of reaction to it, and a "that's just what teenagers DO" kind of mentality. They bailed them out when things went wrong. No-one gave them a bollocking. So of course they all just carried on, thinking it was all ok, how they were behaving. 3 divorced, 1 didn't but it came v close and things only changed after an ultimatum by his wife, which she had never given before and never would again - this was his one and ONLY chance to change, and she meant it.e
You DO need to bollock your DC, when they're out of their hangover. Tell them that this is not a bollocking from a parent to a child, this is a bollocking from an adult to another adult and that this is NOT normal behaviour as most people go out and drink without ended up in A&E. If they don't concede that it isn't normal, they are in denial and you can probably expect drinking issues further along the line. If they do agree that it's not normal and are horrified at themselves, then ask what their plan is for how they will avoid getting in that state again, and if they need any support from you to do it.