Missing Category

Hello David,
Something different happened today.  I added a product to a category.  The product was not added.  The category no longer shows up in adminor the store front.  I didn't loose all my work as the items were saved in the parent category.  I must have a glitch going on.  Can you tell me what happened.  I don't want to try to add the category again until I know if that is what I need to do.
Thank you