Do I have any options to void an agreement I signed? Can Signa offset my SSDI benefits?

While dealing with severe nerve pain (shingles that attacked my spine) and heavily medicated on pain pills I was sent a reimbursement agreement from Cigna to sign in order for my disability to convert from STD (short term disability) to LTD (long term) with out interruption. It stated that if I receive other income (SSD) social security disabilty my monthy payments will be reduced accordingly. Not a problem, which has taken affect. My issue is that out of the whole document there is one line that stated to fully refund Cigna overpayment for their payments for the retro money I received when I finally got approved my SSD. I do not feel that it was clearly explained as I was under the impression that I had to sign it or I would not get LTD. From the time I was put out of work Jan 2013 I was over whelmed with an abundance of paperwork and documents to complete and return in order to get my benefits. Long story short, I was denied twice and had to appeal. During those times of denials I experienced extreme undue stress and anxiety due to not having any income for numerous months at a time. Cigna disability payments were my only source of income. After loosing income for the second time from Cigna in Jan 2014, for 4 months, the stress was so overwhelming that I had to request a mortgage modification so I didn’t loose my home and spent a week in the hospital for stroke and mild heart attack. I feel after all that Cigna has put me through, I should be able to dispute the validity of the agreement that was signed under duress and being heavily medicated. Do I have any options?