Complete mental blankness!

Good lord! You don't need a traumatic experience to have one of those. Age, at any age can contribute to that situation. Disease as predetermined and as unfair as it can be is another unfortunate factor. Over physical and mental stimulation doesn't need to be traumatic to lead to memory loss. Likewise under stimulation wouldn't be to much help either. Of course there is always alcohol. More than one too many sherbets will always do the job. There are methods, including self choice, but they are all too sordid to mention here.
By the way where did you get those groovy glasses from Doc?