why do some things seem more horrifying in dreams?

Nightmares are a reflection of our rawest insecurities.  As such, even if you distract yourself from your worries during your waking hours, you can't hide them when you're asleep.  

There is no restraint in dreams.  We are free to dream up what we need to see, hear, feel, etc.  In real Life we are conditioned to be very careful and to be on guard.   We don't want everyone to know our business.  So we protect ourselves against the world, and it's negativity or judgement.  But in our "dream world" the only judgement comes through our own minds.  If we know how to analyze dreams, we don't have to  be burdened with anything negative in our dreams, as they are only symbolic.  We learn as we go. 

Not, that is not just you.

People wake up from dreams and are physically shaken...traumatized, scared, sweating, they scream in dreams, etc.

Daniel had dreams that were so overwhelming that it made him sick:

Daniel 8:27

And I Daniel fainted, and was sick certain days; afterward I rose up, and did the king's business; and I was astonished at the vision, but none understood it.

The spiritual dimension is real, and all around us. Your soul / spirit sees and lives in that spiritual dimension, and when you dream it is often your soul / spirit that seems things. Your five senses are magnified many times over in the spirit. For example, in the natural dimension you can have poor vision, but in the Spirit you can see with 10x more clarity than normal.

That is makes heaven and hell so much more powerful.

The joys of heaven are many times more pure and joyful that anything you can experience here on earth. On the other side, the terrors of hell are also experienced 100x more clear and vividly.

There are demons scratching, biting and even raping women there. They use evil tools to torment them. Your brain cannot imagine what they see and feel. But if you go to YouTube watch the videos of Mario Martinez, Mary Baxter and Bill Wiese it will give you an idea. They explain how much vivid and real everything looks like and feels like.

With all this being said, I am praying and hoping that you will repent of your sins and ask Jesus to wash you clean. That is the only way to avoid going to that place. He loves you very much, and he wants a very close and personal relationship with you. Seek him.

I have seen blog posts from women that He has taken to heaven and back, like Tara Dulin, and like you said, the wonders of heaven are so vivid, pure, awesome beyond belief. She explains that.

Whatever you do, never ever cross the bridge to eternity without Jesus Christ. Those who are in hell are seeing and experiencing everything in a magnified manner, and they will never get out of there.

Ask a psychologist or try the psychology forum.