Hello 4-ch.
During a quiz or test, my mind simply shuts down and I can't use any of the knowledge I've gained beforehand. It's as if my mind is in a fog or something, and I can only access immediate information or very basic ideas. Even if I've done review assignments and gotten a good mark on them, when it comes to tests, the same thing happens over and over again. I've had this feeling for the majority of high school/college. Is there any way to treat this, or should I just get my ass in gear and start SERIOUSLY studying? (I'm pretty relaxed about studying).

SRSLY studying probably isn't going to help, you have to learn how to retrieve information when you need it. That's the main problem you're having, studying isn't the problem information retrieval is. I probably just spelled retrieval wrong. A common problem with pulling that information out when you need it is that it may not seem important to you, or you can't relate it to anything you're good with. When you study, try to alter your notes so they relate to whatever it is you're good at, or something that gives you a deep interest, that will make you more interested in reviewing notes and easier to remember it because you'll be thinking "Hey I know that answer, it's like how the capacity of RAM increases incrementally by adding it's current capacity to itself!", but that's just an example.

Your problem is anxiety.

Practice relaxation techniques, as well as making sure you are well prepared for tests

Talk to the counselor on your campus, this is a really common problem with students and one they deal with regularly.