I got on SSI several years ago, but for other health issues. My initial application was denied. The state assistance office people told me this was usually the case, but that you should appeal if you had a good case. They also said it would be best to have an attorney to help, and that the wait for an appeal hearing in my area would take about 18 months. So I appealed the decision, and got a Legal Aid attorney, as I had no money to pay a commercial one. In the mean time I was on state assistance and had qualified for Medicaid. I used the Medicaid to get doctor appointments for all my health problems. I even found out I had cancer, and had surgery and radiation treatment while waiting for my appeal. Medicaid covered all except a few dollars of it, but I used my state assistance to pay those few dollars. The state assistance I was getting was about half what I am getting now on SSI, and wasn't enough to pay all my living expenses. I rent a trailer from my parents, so they gave me a temporary big price reduction until I could qualify for SSI, but I had trouble paying for bills and other expenses until then. I had no big debts and don't waste money on gambling, booze, tobacco products or illegal drugs, but the amount of money from state assistance was really not enough.
After about 18 months I finally had my hearing. My attorney had helped me during several visits over that time. She had compiled copies of my medical records from all my doctor visits that I made while waiting for the hearing. This meant that I had plenty of evidence to present at the hearing. Thanks to my attorney's help, and all my medical records I won my appeal hearing, and qualified for SSI. I think it took a few days for SS to get me in their system and start making payments.
When you have filed for SS benefits, and are appealing a denial, if you later win your case, they have to pay back benefits dating from the date of your application. Because some people have substance abuse problems or are just bad at managing money, they don't give you the back payment in one lump sum. They break it down into several smaller lumps and pay them out over the course of a year or two. If you had a Legal Aid attorney or an attorney working on contingent of getting paid only if you win, then SS deducts the attorneys fees first, to pay the attorneys that helped you.
If you have applied for SS Disability assistance, and have been denied, do appeal, but definitely do get an attorney to help you out. I don't know enough about how to handle any kind of legal case to have handled it on my own, and the same holds true for most other people. You really need an attorney to help you navigate the system. Also, while waiting for your appeal hearing, see doctors for all of your health problems, so you will have evidence to support your case at the hearing.
If you are denied again at the hearing, you can appeal again, and again, and keep appealing, but you need to have medical evidence to prove your case or you will keep getting denied. So see the docs so you will have medical records for your case.
Hope this helps. 