Can I Unhide a Folder?

[Paulbud]

Two folders that I use very often are suddenly 'hidden.' I can see them and use them only by going to View, Show Hidden Files. After enabling 'Show Hidden Files,' the file names are dimmed and the screen is populated with every other 'hidden' folder and file. It's not an emergency because I can still use the folders, but why would two folders become 'hidden' and how can I reverse that? Thank you very much