restore lost users?

I seem to have lost me users?

I have very few, but they tell me that they are not getting notified when I post. I looked in the user area and admin is the only one listed?

I have incremental backups and was wondering how I would go about restoring the users? Like I said I only have 5-6, so it really would not be a big deal to just contact them, but thought I would try to learn more about what might have happened and hopefully avoid it in the future

thanks,

Henry