Correct me if I'm wrong but, it sounds like what you are trying to describe is a 'feeling of unreality'. Is that right? The other part that you mentioned, near the end of your post reminds me of how I feel when I shift to another personality who not only feels different but, has a different look in their eyes. When looking in the mirror it is unmistakable that someone else is in the driver's seat.
Another thing that I ran across while doing a search on dissociate -because I like to understand whatever I'm reading and try to get accurate definitions- was a symptom explained as "Feeling that people are automated and inhuman". This is something that has bothered me since early childhood and lead to much speculation on who I am and if other people are really real or not, a while back I did come to accept others as real beings with real feelings but, the suspicion that that may not be the case always lingers in the back of my mind. This has lead to some pretty 'out there' thoughts with me, trying to make sense of it all. That and I have a questioning, analytical mind that tends to dwell on things. I'm never satisfied until I have the answer or think that I have the answer.
So, does any of this make sense to you? Does any of what I said sound familiar?