Subpoena to Attend & Testify?

Contacted under false pretenses by an atty representing someone in a civil action. A real estate settlement & the buyers are suing one another. Time of settlement was more than 2 yrs ago. I had a stroke & a fall resulting in permanent disability, am under physician's care. I explain I can't attend deposition yet he in the hopes I "may" remember something issued a subpoena any way (title co. already attended, file is in A-1 condition no inproprities on behalf of myself as the closer or the title co) yet he is insisting someone may have overheard something in conversation, etc. my physician wrote a strenuous letter detailing my condition & that stress is elevating BP which he fears will bring on another stroke. Details current cond. list all diagnosis & meds am taken incl. pst traumatic stress. I have no memory of closing. my atty sent health ltr & his ltr back 2 this atty stating I can't attend it's dangerous 4 me. What can happen when I don't show