Disability Disclosure in the Workplace?

I just left work because I was having a panic attack.I have GAD and ADHD. I work in retail and I am almost 19 and in university. I need this job to pay for school and other things, but I don't know how much longer I can work there. (quitting and getting a new job doesnt seem to be an option right now as EVERYONE I know is looking for employment) I have 3 managers and a keyholder. I love one manager and the keyholder. The other two I dont really get along with and just tolerate and they always seem to make me suffer and bend over backwards just to do simple things such as book off work for exams. My question is how can I continue working feeling panicked and out of control all the time? Should I tell my main manger (the one i like) about my disability? I tried last week at my review but it didnt seem right and I was nervous. Some part of me thinks it's not their business and I dont want to tell them about my personal life. And on this topic. Should I talk to future employers about my issues? I plan on going into the mental health field (it's what im studying in uni) but I dont want to be discriminated or not chosen because I have a disability as well. :( I'm really just REALLY confused and just know I feel really horrible when I'm at work and want to change it. I am going to a doctor this week as well as my disabilty consultant at school. It's just I have work again Wed morning and I dont know if I'll have time in 3 days to sort this all out.

Please dont be rude as this is a serious matter, and dont say if it's so serious then dont post it on yahoo answers...

Thanks to all of those who are kind!! :)