Terry, sometimes the mind's short-term memory storage function (think DVR) doesn't work properly for a (usually short) period of time. An extreme example is an Englishman named Clive Wearing. There are several documentaries about him and his condition. Basically, his short-term memory is a continuous 7-second loop.
More common is a brief episode of say, an hour or two. Someone I know personally had this happen to them, only once as far as I know. When he "came to," he was completely blank about the last few hours. Scared his wife to death! The weird part is that he had been completely functional and apparently normal during the episode. Doctors never did find a definitive cause in his case, but a couple of possible causes are micro-strokes that self-resolve and something called a TIA (transient ischemic attack).
Something similar happens when someone is administered a "date rape" drug.
If this happens again, Terry, I strongly recommend that you get it checked out right away. It could save your life.
Good luck, my friend.