St. Raphael is a favorite of mine.
There is a website, and I’m sorry I can’t give you the address, it’s not printed on the materials I ran off. You can google “prayers to St. Raphael” and will probably find it
There are prayers for healing, safe travel, happy meetings, mates, and a litany to St. Raphael. Nothing specific to nightmares. However, you can use the prayer for healing because you can insert an intention. It can be said for 9 or 21 days as a novena. I’ve printed the prayer for you below. Or, you can make up your own. The main thing is the prayer, not the fact that it’s worded a certain way.
St. Raphael Prayer for Healing
Glorious Archangel St. Raphael, great prince of the heavenly court, you are illustrious for your gifts of wisdom and grace. You are a guide of those who journey by land or sea or air, consoler of the afflicted and refuge of sinners. I beg you, assist me in all my needs and in all the sufferings of this life as once you helped the young Tobias on his travels. Because you are the “Medicine of God”, I humbly pray you to heal the many infirmaties of my soul and the ills that afflict my body. I especially ask of you the favor of______________________
______________ and the great grace of purity to prepare me to be the temple of the Holy Spirit. Amen.