I have been tanking (WAR) since right before HW. I STILL get a little nervous for new content and even queue for savage completion runs. I look back on how dreadfully nervous I was the first time I tanked Sastasha and laugh. Good times. You'll look back the same one day. Anienai gave you some really great advice. Something that works for me is to study dungeon bosses and primals before my first encounter - it helps to take the nerves off some as well. But remember to have fun and enjoy. There are some incredible sights and players in this game that outweigh the crabs you will inevitably encounter. Good luck!