I just realized that severe depersonalization started with me at 14 and I have no clue why. But things did not register, I felt like I was watching my life instead of being a part of it, I was out of my body, I did not receive any enjoyment being around friends or family and all of a sudden I had no clue how to act or what to say anymore. (Prior to 14 I was the exact opposite.) Depersonalization or Dissociation is supposed to be linked to trauma. (I really can't think of any major trauma that I went thru at 14.)

Personally, I think very poor concentration can cause a person to "drop out of it". I get this feeling like the energy source in my head just won't kickstart no matter how hard I try and I just can't keep up with people socially. I have no problem reading or writing though. Clinical depression does have a profound effect on mental/physical energy.

There's also a symptom in some mental disorders like schizophrenia where thoughts "trail off" (during the middle of sentences you lose your train of thought and can't retrieve it). I had this symptom for yrs and yrs and I can't explain why I had it. (This definitely causes confusion and makes a person feel lost, frustrated.)

http://www.strangerinthemirror.com/dissociative.html