Unless mistaken the same part of the brain controls (the control of) impulses coming from the emotion thingy or something like that

so while asleep the part of your brain which you forged your personality in is asleep leaving your real personality to run wild.

The impulses you have in your dreams are the same intensity as awake but you have no control, so the personality you have in dreams will be the one that becomes your active personality when awake IF that part of the brain is damaged.

I think