Hi there.

There are any number of factors you need to share with us before we can give you a well rounded answer, but I'll do my best.

Are you seeing them when you're awake or asleep?
Why do you assume they are demons?
Are you taking medication that could have hallucinations as a side effect?
How long have you been suffering from this trauma?

I'm not saying I don't believe you- I have seen all manner of things on my journey through this world- just that it is important that we work through some of the more likely scenarios before we make that assumption immediately.

Anything you have that you're prepared to share, I'm prepared to talk through with you.

T'is a scary enough world as it is, especially if half of them think you're mad.

Mike

What I think you're referring to is Clairvoyance, and like pastlifewizard states, there are a number of things a person would need to know to better answer your question. 

That said, if you feel you have the talent, there are a number of ways to develop or train it. 

I would start with Tattwa skrying, for whose techniques can be easily found online.  I will be posting some beginer skrying exercies on my website soon too, if you happen to stop back by this site:

www.templeofthemindseye.proboards.com