Did you say something??
This very well can be MS related. I have found that this happens to me if I am very tired mentally. I have asked my family members to write things down for me that I need to remember. I also have many sticky notes surrounding my computer monitor.
You can do brain exercises which help. There are some video games which are quite specific and university studies have shown these to actually work. My sons both have portable gaming devices and the brain exercise game is designed for them. There are also some apps for smartphones/iphones/ipad etc.
I am reminded of the story of an elderly husband and wife. The husband told his wife he was going to get some ice cream. She said "please get me some Rocky Road". When the husband returned, he had bagels- cinnamon and raisin. His wife was angry and told him "you always forget, I told you I wanted blueberry! Laugh it off and enjoy another day.
It sounds to me like you were exhausted. You should also remember that our short term memory needs to be replayed in our heads before it is saved in our long term memory. Your nap could have interrupted the memory transfer and your short term memory was wiped clean. You are not alone in this!