why is this so hard to deal with?

okay so I have suffered from anxiety disorders since I was 11 years old and I am now 17. there for a while I was doing okay on Prozac. But about 6 months ago I stop taking it and now I feel that that was a bad choice. Today just randomly I got really nervous and felt like I couldn't breathe. I seriously felt like someone is choking me I cannot breathe. I was getting oxygen through and I knew in my head that it was just anxiety but it is so scary having that feeling is there anyway I can make this completely 100 percent stop. It scares me so much and I can't do anything with sides think about it it has became a big problem. since I've been hyperventilating I feel like all my muscles are so tense and that I'm so tired and week but I still cannot stop thinking about it. If you have any advice or any tips from having anxiety it would be greatly appreciated. Please help me :-(