You wake up in the morning after a night of drinking with friends. You did not want to drive drunk, so you slept on a friend's couch. You roll off, drag yourself out to your car and start heading home.
Then you get pulled over and the officer arrests you for drunk driving after you fail the field sobriety tests. You admit that you were drinking, but it was yesterday. How could you still be drunk?
It's definitely possible, even though a lot of people don't realize it. For one thing, you may think of that as "yesterday," but how long did you stay up? It was probably actually "this morning." If you only slept for a few hours, you could very well still be intoxicated. Sleep doesn't magically cure you.
What does? Time. That's it. You need time for the alcohol to pass through your system, and then you'll sober up. Some say that it takes roughly two hours per drink.
Now it's time to do the math. How many drinks did you have? How many hours were you asleep? If you were severely intoxicated just a few hours ago, you could be over the legal limit in the morning. Different personal factors also play into it, such as your tolerance for alcohol, your weight, your gender and much more. But it is possible.
Getting a DUI after you deliberately tried to avoid one is frustrating. It can also have a massive impact on your future. You absolutely need to know all of the criminal defense options you have at your disposal.