How to decide to apply for disability or try to work part time?

I am currently off on a sick leave because my lupus is not under control and I am experiencing re-occurring infections that are a side effect of my Benlysta treatments. I recently have got problems with my heart and ischemia from vasculitis in my brain. I have been struggling very hard to work the last 2 years missing many, many days and basically spend all of my energy on work (weekends and evenings in bed). I just keep trying to hold on thinking maybe I will get better. I have to decide to either go back part time or apply for long term disability. The thing is if I go part time I loose my benefits and if I am successful in getting the long term disability then I keep my benefits. I never thought I would be considering applying for disability at 32 yrs old. How have others made these decisions, are there any solutions I am not thinking of? I am afraid to apply as so many people seem to be denied and I worry about the financial aspect, plus I love my job and feel like I won't know who I am without it. I wish I could make a decision and be at peace with it.