Submitting a plugin form to database in admin page

[UPDATE]
You should have the page divided in two section-
1. One dealing with AJAX request and Post Method
2. Displaying form data

Here is outline

<?php


if (strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) == 'xmlhttprequest'  or $_SERVER['REQUEST_METHOD'] == 'POST'){
// Process AJAX Request or POST Method
}
if (strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest'){
// HTML Code here which will not be returned to AJAX Call
}
?>

As html code will be returned with ajax response that will cause trouble if not filtered.