If you’re having nightmares, you need to start reading something a little more literal and cheerful. All of the Bible is good to read, but there’s a time for everything. Read one of the psalms praising God, or “The Lord is my shepherd.”
The Lord doesn’t want you to have nightmares.
I’m going to point you to one of the really old hymns of the Church, because it has a good prayer against nightmares in it. This is the traditional hymn for Compline (the Office at the end of the day), and it dates back to the 7th century. Here’s one version of the song. (There are other tunes for it, but that one will sound a bit familiar!) The monks sing it before going to bed for the night.
Te lucis ante terminum,
rerum Creator, poscimus
ut pro tua clementia
sis praesul et custodia.
To Thee, before the close of day
Creator of the world, we pray
that with Thy wonted favor, Thou
wouldst be our Guard and Keeper now.
Procul recedant somnia
et noctium phantasmata;
hostemque nostrum comprime,
ne polluantur corpora.
From all ill dreams defend our eyes,
from nightly fears and fantasies:
tread underfoot our spiritual foe,
that no pollution we may know.
Praesta, Pater piissime,
Patrique compar Unice,
cum Spiritu Paraclito
regnans per omne saeculum.
O Father, what we ask be done
through Jesus Christ Thine only Son,
who, with the Holy Ghost and Thee,
shall live and reign eternally.
(* spiritual foe = the Devil. The actual words translate as just “crush our Enemy,” but
that’s who they mean.)
Sleep well tonight, and pleasant dreams!