表单提交后重定向用户时页面冻结

In php, I collect information from the form and build an email. I then have the following code redirect the user to a page after a 200 response code.

// Send the email.
    if (mail($recipient, $subject, $email_content, $email_headers)) {
        // Set a 200 (okay) response code.
        header('Location: https://my.website.com/wp-content/uploads/2015/07/a.pdf');
        exit;
    } else {
        // Set a 500 (internal server error) response code.
        header("HTTP/1.1 500 Internal Sever Error");
        echo "Oops! Something went wrong and we couldn't send your message.";
    }

Unfortunately, when I attempt to sumbit a form, Chrome freezes and I have to close the tab. Any explanation for the cause and fix of this issue?