My Grandma Rose also suffered from Dementia.  The signs started slowly then seemed to progress quickly.  Walking through the door of her room in assisted living was a little like walking into a time machine.  I never knew who I would be.  Early on, she knew who I was, then slowly that began to change.  Sometimes I was her cousin, most times I was her sister and less and less I was me.  Watching her memories slip away was heartbreaking.  The Alzheimer's Association helped me learn to "be in the moment".  Whoever my Grandma thought I was that day is who I was for my entire visit. The memories she shared with me during those times are a treasure to me.  Memories I had never heard before about her and her family, her and my Grandpa when they were first married.  She had such joy when she shared these memories!  Her eyes would light up and she would smile and laugh just like the Grandma I always knew, just "younger".  I left those visits with mixed emotions, sad that she no longer remembered me but so grateful to have learned more about her life and see her happiness restored.