I know exactly where you're coming from. I suffered from chronic sleep paralysis, which were always terrifying episodes (don't think i've ever had a pleasant one). I can EASILY get into paralysis if I wished but i've been so traumatized that I always wussy-out. I consider myself brave, and in real life i'm scared of very few things.. but when it comes to SP I act like a little girl.

You're in a better position since you're experiencing this in your LD, which is way more easy to control with practice (like making scary things disappear) than sleep paralysis. I would suggest reading how to control your dreams, and just keep practicing.

Also, with the whole doppelganger.. my personal opinion is that archetypes are more symbolic than anything else. for example i'm sure your 'doppelganger' can change in different dreams, or maybe over time. It's not like an actual being in your head that stays there forever. Maybe if you over think it and convince yourself that she IS your doppelganger, that she'll just keep reappearing. Just my 2 cents.

Best wishes to you.