$query = mysql_query("SELECT `id`, `max_health` FROM `dungem` WHERE `health` < '10'");

while ($row = mysql_fetch_assoc($query)) {
    mysql_query("UPDATE `dungem` SET `health` = '".$row['max_health']."', `dead` = '0', `dead_time` = '0' WHERE `id` = '".$row['id']."'");
}