I don't like the things I've done

I don't like the things that I've done. I used to be such a nice person. I used to be so happy and up for anything. I used to have so much energy. But that changed dramatically 7 years ago and nothing has been the same ever since. Why I changed is too long of a story, but it was unnecessary and I feel like I hurt the people that meant the most to me because of it... including myself. I'm so caught up in this different person that I have for some reason created that it seems like it's impossible to get out of. I think I really do know deep down that I can be ME again, but find the process to be far too painful and because I'm afraid of making awful mistakes again over my negligence. For the past 7 years I've been someone else and people believe that this is me. I want so badly for them to know who I really am, but in fear that they might see how crazy I really am. I feel like I've been a horrible person, and since I've acted like this I start to believe that I am a horrible person. This makes me feel so sad and alone that at times I find myself holding back tears in public. I lost some very important people who were very close to my heart... I wish I knew then what I know now. I wish that I didn't have to be so afraid and naive. I wake up in panics over this it seems like my heart is always pounding in my chest. I can't make it stop! I want this all to stop I can't handle it anymore! I'm sick of living my life like this. I'm only 24 yet I have heart problems that are probably due to this anxiety. But I feel like if I don't fix my problems then I'm going to keep making the same mistakes and get hurt over and over. So I have to figure out what is going on in my head but I just get so confused. Is there anyone with advice? I don't have anyone to talk to about this.