Demons

If it's from a television show, it's probably fiction. I don't know anything that can effect you in that way, and I doubt that it can.

I can't think of a demon making you sleep if sleep was not already willed on your part anyway, however, contacting an entity through sleep is pretty common. Lucid dreaming can be used for such purposes.

This thread has been moved to Spiritual Creatures from Misc Topics.

There are some spirits that will feed off the energy of nightmares and attempt to cause them as well but I don't think they're all to common anymore.

Ive dealt with nightmare demons in the past. Their not all that powerful, and are even weaker than novices. Their lifespan before they fade is about as long as the person pays attention to them in their dreams. That's why people of the wiccan world generally dont deal with them. But the easiest way to get rid of them is cleanse the crown and third eye chakra.
As for demons who feed off of nightmares, they leave marks on the bodies they siphon the nightmares, fear, and dream energy from. Those are harder to get rid of, since their connection only becomes active when the victim is sleeping.

I've met and been attacked by spirits in my nightmares. They weren't Demons, but there are lots of dream related spirits.

Any spirit can get into your dreams,even a human if they know how to.

Lower beings tend to be harmful to humans because they look forward to consumming the energy we got in all sort of ways to obtain power or to heal themselves.

High ranked demons do not seek such things and can be great spiritual guides. But I do not suggest you to summon any before you get more advanced.

You will need to know to direct and sense energy well beforehand,and also how to communicate with a spirit. Background info about the one you will to summon is also advisable.

I hope this explains it. "Bill" is fictional ;)

There are many demons who can contact you through dreams, incubbi and succubi in specialty.
Demons are not to be feared, they are highly intelligent and misunderstood.
I will post a list of demons for you here, all you can contact
http://www.angelfire.com/empire/serpentis666/DEMONIV.html

Hope this helps!

I LOVE GRAVITY FALLS!

I watch the show too. Bill Cypher is a creature that exists in an entirely different world. The only way he can join us is if you break the seel that binds him to his world, or create a bubble where both worlds are present. His world is the dreamscape. This is a world above us where objects and creatures are not bound to the same rules as us. The bubble creates a cross between worlds. There he can exist in our world without leaving his own. His dream based powers form when you enter his world. There, the rules don't apply, so you can do anything based on your thoughts