Sidebars No Longer Showing on Appearance>>Widget page

Normally when I go to appearance, then to widgets, it shows all of my sidebars including my custom sidebars (custom sidebar plugin). Suddenly, they're all gone! All of the sidebars still exist because they are showing up when I visit the posts, but I can no longer access them to make changes or new ones. If I go in any post in edit mode, when I go to 'post sidebar' on the right side and click the down arrow, it still shows every sidebar I've created. So weird! Can anyone help? 21stcenturymom.com