Amnesia, that favorite device for authors, is a symptom. There are many forms, but the most familiar to all of us is one of two. Anterograde or Lacunar. The first of these means simply, the loss of memory of past experiences. The second, means loss of memory of isolated events, or a 'gap' in memory - patchy recollection with sudden blanks. It's a common effect of having a little too much to drink, and then, like John McCaffrey, you wake up one morning with that terrible knowledge that somewhere the night before you can't remember what happened at all.