In a way it reminds me of demon-possession scenes from books and movies.  Have you been influenced by anything like this lately that might trigger a dream like that?  Perhaps you watched a scene or read something that scared you, but you didn't want to express the fear in real life, so you enacted something scary in a dream.

One possible idea about this "other half" character is thinking of this as the "shadow self," a term that we've thrown around on this forum and other places.  Basically, the idea is that we all have a sin nature, a "dark side" of us that we try to keep hidden.  It is still there, though, and if it can't find ways to express itself in "real life," it might show up in a dream as an evil creature that wants to control us and/or harm us.  Sometimes it shows up as someone we're fighting with.

I find it interesting that your two best friends have names that are homonyms (sound exactly the same, but spelled differently.)  This makes me wonder if the dream is not using them as literal people, but as symbols.  i.e., using two people to express the same concept.  Maybe it's coincidence, but it seems to me that they might be two sides of the same aspect of your personality.  The "best friend" symbol in a dream is often simply a representative of another aspect of our self.  Kind of like we have right brain/left brain that are unified as one, often the "you" character and the "best friend" character are simply expressions of the "whole self person."  (these are my terms; specialists might have better names for these ideas.) 

Anyway, the two best friends might represent the "best friend" character of a dream, who are watching in concern as you undergo dramatic change in personality and sickness in body.  I wonder if you feel like part of your life is falling apart, and you are spinning out of control.  There's a sense in which you feel like you are watching life happen to you, and even though you're trying to take care of yourself, it doesn't seem to be working.

It's been awhile since the original post; have you had the dream again?  Has anything else developed that might shed more light on it, or give it another angle?

Best wishes and prayers for you in this stressful season.

I'm so sorry to hear about your physical problems!  I'll pray for a quick recovery.
I have gone through some physical issues that, as it turns out, were connected to malabsorption of vitamins in the digestive system.  Turns out that many common foods we eat can make our bodies much less able to absorb the vitamins we need, even if we are eating them.  I found a lot of helpful information on this website:
http://dogtorj.tripod.com/index.html

My family is on this diet recommended by this website, and we have seen great improvements!  Maybe it will help you too!