A concussion is when you suffer physical trauma to the brain. That is to say, bouncing your skull off the wall hard enough that your brain hits the inside of your skull, and is injured in the process.
This is characterized by cognitive impairment. Difficulty tracking moving objects. Difficulty processing information. In some cases difficulty speaking, or remembering stray trivia, like who the president is, what year it is, or your name.
So, it sounds like the ER was right, you probably didn’t suffer a concussion. You fainted, bounced your skull off the floor, but your brain wasn’t actually injured in the process. It was there to tell you, “well, that sucked. Get up, let’s not do that again.” And, here we are. Blow to the head, no concussion. It happens. It’s unpleasant, but it does happen.