that happens to me a lot, I have found reassuring self talk helps, saying to myself what I might say to a child who has woken from a bad dream, like "I'm OOK, everything will be alright, God's got me, this too shall pass..." focusing on your breathing, blocking out other thoughts works too. If your anxiety is spilling over the top tho, I'd way talk to your doctor, sometimes we need some extra outside help, its possible a low dose anti anxiety medication would be helpful.