försök detta add this to form onsubmit ="return submitform();"
function submitform(){
var comment = $("#comment").val();
var alertid = $("#alertid").val();
$.ajax({
type: "POST",
//url: "ana.php",
data:{cmt:comment,alert_id:alertid}
}).done(function( result ) {
$("#msg").html( result );
});
return false;
}