I know that feeling... will get my vit B12 checked. Figured it is just my flat feet reminding me to wear shoes :)
Could be either, both or neither, but seems like a good thing to check. And you have a story about it too; that you have flat feet and should wear shoes. It's interesting the stories we tell ourselves.
Just a thought: if you live with a young child and take naps, be sure to check if there's a piece of yarn tied on your toe.