Hi, I'm sorry you have to go through all of this. You're right, this really does suck. I was in your place at about your age as well. Derealization is pretty scary and it is really hard to understand. For me, derealization was a side effect from depression.
I also have an anxiety disorder that used to run my life basically, especially in high school. I would have panic attacks at school all the time and a lot of the time I'd go to the nurse pretending to be sick (my anxiety symptoms made me feel like I had the flu- nausea, muscle aches, feverish feeling) so I could go home. If you're in class and feel an anxiety attack coming on, because you're in school and can't really distract yourself- the best advice I have is to take slow deep breaths. Breath in as slow as you can and once you've taken in all the air you can, hold it for 3 seconds and then slowly breathe out. When not in school though, try and find little things that make you feel better. For me, I discovered that reading really helped my anxiety. It sort of forces me to go out of my own world and concentrate on someone else's, which eased my anxiety. Other things you could try are drawing, running, watching a movie, taking a walk outside, etc. I really recommend taking a walk, it helps clear your mind and there's a lot to see around you that can get your mind away from panicking.
As for depression, I'm still trying to figure out myself what helps. Honestly, when I'm feeling really depressed sometimes I put on some really sad music and just cry really hard until I can't cry anymore. Then for some reason I tend to feel better after that. Having a good cry is healthy sometimes. Running seems to really help me as well. It does release "happy" hormones so there is a science behind why people feel so good after runs. Surround yourself with friends and family, distract yourself with a hobby or a sport, etc. Different people tend to find that different things help them.
I really do believe that you will get through this and be happy one day. I've struggled with horrible, crippling depression and anxiety that was so bad I would have multiple panic attacks every single day and I felt like I missed out on a lot because of these issues. I never thought I would be happy, but I did get there. Now, my anxiety only shows up once in a while. I think a big part of that was really knowing the anxiety and myself. Recognizing the symptoms and remembering the tiny things that helped. You will get there and be happy, I promise! You seem pretty intuitive of your feelings now and that's a really good trait to have. Be strong, know that you are absolutely not alone in this, and fight this!
Thank you a lot, I honestly really appreciate this. I will definitely try the breathing thing you said to do in school. I am fighting it and I feel normal sometimes, then the next second, completely miserable. But thank you, and I'm going to try some of the things you said!