All successful form fields are submitted to the server. CSS display does not impact whether or not a form field is considered successful. The HTML spec defines what makes a control successful.

A successful control is "valid" for submission. Every successful control has its control name paired with its current value as part of the submitted form data set. A successful control must be defined within a FORM element and must have a control name.

However:

• Controls that are disabled cannot be successful.
• If a form contains more than one submit button, only the activated submit button is successful.
• All "on" checkboxes may be successful.
• For radio buttons that share the same value of the name attribute, only the "on" radio button may be successful.
• For menus, the control name is provided by a SELECT element and values are provided by OPTION elements. Only selected options may be successful. When no options are selected, the control is not successful and neither the name nor any values are submitted to the server when the form is submitted.
• The current value of a file select is a list of one or more file names. Upon submission of the form, the contents of each file are submitted with the rest of the form data. The file contents are packaged according to the form's content type.
• The current value of an object control is determined by the object's implementation.

If a control doesn't have a current value when the form is submitted, user agents are not required to treat it as a successful control.

Furthermore, user agents should not consider the following controls successful:

• Reset buttons.
• OBJECT elements whose declare attribute has been set.

Hidden controls and controls that are not rendered because of style sheet settings may still be successful.

Disable the form fields you do not want submitted.

$('#category').change(function(){
    $('.sub-category').hide().prop('disabled', true);
    $('#' + $(this).val()).show().prop('disabled', false);
});