Everything he thinks and talks about is regarding death. Paxil is an antidepressant from the class of drugs called SRI drugs. This stands for serotonin reuptake inhibitor drugs. They are generally well tolerated, but some patients experience difficulty sleeping, dry mouth and constipation. Cognex is a relatively new drug, especially for the treatment of Alzheimer's Dementia.
Side effects are mainly liver and white cell depression.
Trazadone is an antidepressant which is in a class of its own. It also works primarily through serotonin. I would be very reluctant to combine Paxil and Trazadone since they both work through similar mechanisms. The only way to determine if the problem is his dementia or the drugs is to systematically stop one drug at a time. I'd start with the Trazadone.