Please help me.....flight fear?

Ive got a nonstop flight from houston to munich on the 2nd. It is 13 hours. I am really scared, I cannot sleep at night because of how scared I am. Im afraid of DVT because they say it can happen to anyone regardless of how healthy they are. lol. Im 20, and 5'1, and def not overweight. I am still nervous though...Should I be? I plan to walk around the cabin every 30min to hour...any advice?