After being on Donepizel for 4 years, then recently having an low b.p. episode (o/n in hospital) but now cleared by Cardiac Dept, they have changed Dad's (aged 92) meds to Mamantine. The effect has been dramatic - sleepy, non mobile, seemily depressed. I can't see the advantage of this and would prefer him to go back on donepizel even if a higher risk factor. Brothers and I have POA. any thoughts?