If I didn't sign anything, do I still have to pay mony back to a former roommate? I had a stroke and am not working.

From your email I gether that your former roommate loaned you money, althoygh you don't say wo explicitly.  If so, you are obligated to repay it unless it was a gift, or unless you received it (or someione received it on your behalf, like a creditor of yours) as part of a contract in which you provided something of value in exchange for the money.  The lack of a signed document doesn't change anything, except that it may make it harder for your former roommate to prove his/her case.  You would still be liable to repay the money, even if you can't work, unless the debt is discharged in bankruptcy.