If you have medical documents to prove your mental/physical issues and possibly proof of poor functioning at work (and/or multiple absences) you will get SSDI. I think everyone is automatically turned down when you apply then you have to appeal and go to Court (about 6 mths). That's what happened to me (been on long-term SSDI 2x). SSDI $ amount is based on your age and education.

My first court case (2004) was partially favorable. I asked for backpay (ie. when my disability first began: one yr before SSDI application) and only got 1/2 of what I asked for. We appealed again, same Judge denied me, the SSA Appeals Council overturned the Judge's decision (Judge did not look at my paystubs for absences) and I got all backpay that I asked for. I had an excellent, sharp lawyer from Princeton. (fyi: Every Court decision is sent to Appeals Council for review for checks and balances.)

Get a very good lawyer. My lawyer told me that he would rather take mental disability cases than physical cases because they were easier to prove. (I had medical records going back to 1990 to back up my mental disorder.)