First off dreams occur in REM (rapid eye movement) sleep or stage 4 sleep according to the new classification by the American sleep association. The brain activity of stage 4 or REM sleep is identical to the awake mind except that the body and voluntary movement control is inhibited by a part of the brain.
We also know that medication can induce nightmares or strange dreams or suppress them.
Sleep specialists readily admit they have no ideas what dreams are.
There have been a variety of psychological theories about dreams, but none of them can explain why some dreams reveal future things or seem to offer us insight into present things, or warnings of things that need to be changed in our lives.
In my perspective, Dreams were just one way that man communicated with God. When man fell by eating from the tree of good and evil, evil was allowed to enter man’s DNA and his dream life. Thus, our communication with God via dreams likely became very unreliable and in a way, mirrored the spiritual combat that takes place in our awake spiritual lives. How to interpret a dream requires discernment, skill, experiences, grace, prayer, and a few other things likely.
One day after Jesus comes back, I believe that man and nature will be restored from the effects of the fall, and dreams maybe something that likewise becomes healed and well.
Sadly, man is not the only created being to fall. There are fallen angels as well. We know that angels can communicate with the mind of man in a dream, as the angel that gave St. Joseph his warning to flee to Egypt and to marry the Blessed Mother.
It then makes sense that if 1/3 of the angels fell, some of them retained this power, and now use it for evil.
That all being said, God can still give a dream and there are people who claim to be able to interpret them.
One such man is John Paul Jackson, someone I have never met, but have been studying his materials of late.
Jesus spoke to early christians in parables and metaphors. He still does in dreams.
Apparently, according to John Paul, spiders represent the occult or occultic forces or demons of the occult.