I've got several anxiety disorders and Generalized Anxiety Disorder is one of them. GAD, to me, means that I'm constantly worried about things. All kinds of things. I overthink things and I catastrophize a lot. For example: "I don't really understand what the lecturer is saying right now. I'm so stupid. Holy crap, what if I fail the exam? What if I fail and I'll have to drop out of university?! Great, I'll never reach my goals. I suck." The anxiety then leads to it being very difficult to focus, which in turn leads to more anxiety. It's like the vicious circle from hell. My GAD not only makes me worry about my studies though, but also about other things such as being late to the bus, the bus being late, not knowing exactly what's going to happen all the time, worrying about not having enough money etc. My other anxiety disorders (social anxiety disorder and OCD) contribute with a whole lot more anxiety but often about other things.

My anxiety disorders make it very difficult for me to function "normally". Sure, I manage to study at university but my disorders really limit me and make me live in fear. Constantly. A little bit of anxiety is normal but when it's constant, excessive and it's taking over your life and thus prevents you from living the life you want to live, it's unhealthy and that's when you should probably go check it out.

There's a lot more I could say about this but I think this is enough for now. Hope it helps!

EDIT: I should add that I'm in no way an expert on these things. I'm only writing out of personal experience.