You go out for a couple drinks with your friends...and of course you've pregamed with a few shots...and then there's an after party...you wake up. Zero memory of what happened after 10pm. You think back...but no, the last thing you remember is getting to the bar. You don't remember anything that happened at the bar or who you talked to...did you go to a second bar? A third? Did you order food? You snatch at your phone and reread any texts you might've sent last night looking for clues in desperation...this, my friends, is a blackout.
The day after you've had one you probably want to call up all your friends who were with you so that you can start to piece together how you behaved the night before and if anything out of the ordinary happened. You should also read through your texts in case your thoughts, as reflected in your private text conversations, didn't reflect your actions. Then you can go about nursing your hangover with excessive amounts of water, minimal amounts of sunlight, and some grossly comfortable clothing for you to slob around in while you try to figure out if you fucked your own life up last night.
Alcohol impairs the brain's ability to take things from your short-term memory and story them in your long-term memory. Sometimes with a blackout you are capable of cued recall, which means, if someone reminds you of what happened, the memory comes back to you, but you wouldn't have been able to remember it without the reminder. Blackouts are more likely among people with anxiety disorders. They're also more likely to occur when your blood alcohol level increases very rapidly. In other words, if two people were drinking, and one person had a few drinks very fast and the other person had more drinks but in a spaced out way, the fast drinker would be more likely to black out. There is no "once I drink x amount I will black out," but rather it is a matter of how quickly you drink.
What's most frightening to me is that, once you've had blackouts before, the next blackout will come more easily. Similar to concussions, once you've damaged an area of your brain with a concussion, it takes less pressure or force to get the next concussion. As you allow yourself to black out numerous times, you are actually impairing certain neural networks that work with memory, and making it easier to get the subsequent blackout. You do not have to be an alcoholic or have liver problems to black out. Frankly, you just have to drink too fast.
What you've got to learn is that drinking is not a race, and you can be a raucous, grand ole drunk without forgetting any moments of the night. The first key is to drink slowly. Maybe if you had let two shots hit you, you would've realized you were a good level of buzzed you want to ride out, but instead you drank three and now...you're blacked out. So, let each drink hit you, drink wine and beer and anything mixed slowly, and if you take a shot, give it some time to hit you before you decide what you'd like next (and the answer can always be water!). Speaking of water - have food and water. Water will keep you hydrated and prevent headaches the next day, but having to drink the water and pee it out during the night will also slow you down. And food will also help slow you down and feel less hungover the next day.
While you may think you're a nice, docile drunk, you are not in full control when you are blacked out. If you were in full control, your brain would be functioning at full capacity, but clearly it is not, since your brain has completely forgotten how to find your long term memory. With you're impaired functioning you could make poor decisions as simple as spending too much money at the bar to decisions as disastrous as drunk driving or engaging in unprotected sex. Vandalism, property destruction, getting in a fight, etc, could all also be consequences of what was supposed to be a good night out.
Video: Why Do We Get Blackout Drunk?