adenocarcinoma

Hi, my fiance was diagnosed with Stage 1 metastatic stomach cancer and adenocarcinoma in the intestines. He had surgery on May 29th and the "bad" parts were taken out. Surgery had taken a toll on his health physically and now he is very weak. He started chemo and radiation a few days after. Just today I received a word that he had been having seizures since morning and the doctors are afraid he had some kind of a stroke, which I am puzzled as he didn't have any heart problems and was physically fit, as far as i know since he works in the military. Is this a common effect of the treatment or should I worry?  What are the chances of him surviving? Please help, I don't want to lose him, not now and not this way...