On a layout (with or without a tab), a field is a "view" of the data. If you have access to the layout, you can put the field back on the layout and the data will still be there. If, OTOH, you have access to define a field and have deleted that field, the data would have been deleted as well. I don't think you deleted the field, just the "view" of the field on that layout.
This help topic may help you. Follow the links within the page, as well.
Removing fields from a layout does not remove the fields from the table, so all the data is still there. Just put the field back on the layout.