What scares you the most about the prospect of having dementia in your later adulthood?

What scares you the most about the prospect of having dementia in your later adulthood? (Please be detailed and comprehensive in your answers). 

Have you ever witnessed the onset and ravaging effects of a form of dementia in someone you know?  What is/was it like for them and for those close to them?  What changes occurred in their life? 

If you had access to the genetic test for Alzheimer’s disease, would you want to take it?  Would you want to know the results or would you rather wait and experience the disease when and if it occurs in your life?  Why or why not?