What to Tell My Employer

I've been struggling with what I think is stress induced depression from my high paying job and living circumstances, suicide thoughts/threats, for several years now. I made just under $100k last year, but work a ridiculous amount of hours every week and I am paid salary. Been depressed for the last 18 months, sought out treatment, been on wellbutrin for 8 mos now. My work drive had decreased significantly, my 'I don't give a crap attitude' has increased to the point that my co-workers are taking note and are telling me to get off my ass and get out there. I run my own segment within the company and I have little supervision except when the shtf. So its very easy to get into the habit of not keeping up with the little details, but I still do most of my major duties. My concern is what my boss is seeing by his little comments here and there about my performance but they have not said anything outright about it as in a formal counseling. Which I think may be just around the corner.

Do I make up an excuse about my work performance deficiencies, and promise to get in high gear? Or can I tell them a little bit about what's been going on with me as in my current diagnosis, without them losing confidence in me and termination? In the hopes that they understand and can relate and just back off a little bit. I read on the internet about depression being a disability, and that there is act covering it, and that if an employee discloses the disability that the employer by law has to make accommodations to help the employee, (to a certain extent). Is this true, has any one disclosed the issues to their employer? Thoughts?