You are driving from one familiar place to another and realize upon arriving that you can't remember how you got there. Or, on a holiday trip home to see family, you find you are inexplicably fatigued. Perhaps it's your spouse, who has taken to disappearing for evenings at a time, and you're convinced that he or she is having an affair. Or it is a boss or colleague, who seems to switch to an alternate personality in the blink of an eye. You can never...