Alzheimer Disease - REALLY
I watched my grandmother die from it and felt for my father. It starts off very slow and simple. Try seeing a loved one every day slowly disappear every day and have it drag out for years. Try experiencing going to visit them and they don't know who you are. You visit them and the are out of time and place. They think is twenty years earlier, mistake you for someone else, get scared because they don't know where they are or who your are, can't perform simple tasks, etc....
I hope Will Ferrell educates himself about this disease.