ADA has nothing to do with unemployment. You may qualify for disability benefits. Statements like you just made tell me that outpatient treatment probably isn't appropriate for you. And even with outpatient treatment, you shouldn't be working at first, recovery is a full time job in itself.
Depending on other factors, you may qualify for FMLA so you could return to work when your treatment (or at least the intensive phase) is complete, if it will take 12 weeks or less. Even if you don't, your employer may be willing to work with you in that respect, if you voluntarily come forward about your problem and your desire to get better before your performance completely tanks and they have to fire you.
But really, your life and health is the most important thing. When you are sober and healthy, a whole world of opportunity opens up for you. Don't worry about your job. Go to the hospital today.