Symptoms: Lost two hours today

In anticipation of a doctor's appointment this morning, I was focused on making sure I had a list of Betty's meds handy, and the paperwork related to the at-home doctor visit for my wife. I was concerned about whether I would be able to remember whatever the doctor said during his visit, but he mostly took notes and interviewed Betty. After he left, I "crashed" mentally. As soon as I had completed writing notes to myself about the appointment, I recall my last thought was about what to fix for lunch. Then I "suddenly" woke up, having lost two hours. Still sitting at the computer, I posted the note above before I got up and took a proper nap which lasted until about 4:30 today. I never did remember to eat lunch. I have had a number of long "gaps" in my days recently. I assume I'm generally asleep during those periods, but on at least one recent occasion, I lost 5 hours, and had vague disconnected images in my mind of hunting for my Kindle reader. It had been lost, but when I regained consciousness, it was on my bedside table where I seemed to recall having purposely set it so I would find it when I was awake. That incident was a bit unsettling. I'm not sure what to think about it, but since it has been the only incident in which I know I was active while unconscious, I'm not too worried.