Hmm. That's hard. Do you have favorite bible verses? Maybe after a nightmare, instead of trying to go right back to sleep, you calm yourself down with these, then write down the dream. Have a warm glass of milk, or... I don't know. Create a soothing little ritual you do every time you have a nightmare.
And I like the other suggestions folks have come up with here, too. Try things until something works for you. Oo! One thing that works for me on sleepless nights is lavender incense. I don't know why, but that stuff makes me sleepy. And I admit to occasionally snuggling up to a stuffed animal.