form.php:
<?php
session_start();
    try {
        $db = new PDO("mysql:host=localhost;dbname=arnvan2_arnvan2","arnvan2_arnvan2","ww");

        if(isset($_POST['verzenden'])){
            $naam = $_POST['naam'];
            $email = $_POST['email'];
            $onderwerp = $_POST['onderwerp'];
            $bericht = $_POST['bericht'];


            $query = $db->prepare("INSERT INTO berichten(naam, email, onderwerp, bericht) VALUES(:naam, :email, :onderwerp, :bericht)");
            $query->bindParam("naam", $naam);
            $query->bindParam("email", $email);
            $query->bindParam("onderwerp", $onderwerp);
            $query->bindParam("bericht", $bericht);
            if($query->execute()) {
                $_SESSION['gelukt'] = true;
                header("location:./#contact");
            } else {
                $_SESSION['gelukt'] = false;
                header("location:./#contact");
            }
        }
    } catch (PDOExeption $e) {
        $_SESSION['gelukt'] = false;
        die("Error: " . $e->getMessage());
    }
?>
index.php:
<?php
                if(isset($_SESSION['gelukt'])) {
                    if($_SESSION['gelukt']) {
                        echo "
                            <script type='text/javascript'>
                                swal({
                                    type: 'success',
                                    title: 'Verzonden',
                                    text: 'Je bericht is verzonden en ik neeem zo snel mogelijk contact met je op.',
                                })
                            </script>";
                        session_destroy();
                    } else {
                        echo "
                            <script type='text/javascript'>
                                swal({
                                    type: 'error',
                                    title: 'Error',
                                    text: 'Er is iets misgegaan. Probeer nog eens of neem contact op via info@arnovanliere.nl',
                                })
                            </script>";
                        session_destroy();
                    }
                }
            ?>