My Dad Has In The Last Few Months Started Having

My dad has in the last few months started having loss of appetite, memory problems such as forgetfulness & simple things that he use to know...such as how to fill out deposit slip. he has been under a tremendous amount of stress with his job & we thought maybe the inability to focus, loss of appetite, sadness etc was related to that & we tried to get him to go to doctor but will not. in the last week, he has been c/o headache, dizziness, and inability to get thoughts out, forgetfulness. He still refuses to go to the doctor. my stepmother says he appears to have a shuffle gait at times. He does have history of stroke. he has no weakness on one side. i am concerned & want him to go to doctor but I can't make him. Do you think these symptoms are possible just stress? he does have history of lung cancer also with most recent CT chest as negative. it was caught early last year & stage 1..had lobectomy & all follow up CTs negative. Is it possible this could be alzheimers? I would have thought if it was that it would have been more of gradual signs but seems that things worsened when his job became more stressful. he wasn't eating and was having nausea,those symptoms have improved some. just would like someone's thoughts since I can't get him to go to doctor