I do not believe that I have dissociative identity disorder, but sometimes I feel like I do have multiple personalities, and I'm not sure that's a bad thing.

My evidence: most of the day today, I was working on contaminant transport models - calculating first-order decay rate constants, biodegradation factors, and chemical concentrations in groundwater samples collected at a site over the past ten years.  All these data and calculations were then geospatially synthesized into a 2-D model and simulations were run, calibrated, and verified, and then used predictively.

Look, I'm no Einstein.  This may be child's play to some of you, but my brain isn't wired toward mathematics and analytical thought.  I tend instead to be more intuitive, creative and verbal.  But I'm willing to do the heavy analytical lifting and work my way through the calculations, equations and spreadsheets, even if it doesn't come naturally to me.

But here's the thing - after doing these calculations, etc. for a few hours, the normally verbal part of my mind sort of shuts down and I find it extremely difficult to make small talk with others, to be creative, or to think, as it were, outside the box.  A linear, analytical mindset takes a hold of me, and although all my memories and so on are intact, I feel like I have a different personality.  I feel like I'm someone else. 

My analytical personality is not nearly as likely to crack a joke, engage in whimsical thought, or find comfort in music as my creative personality.  My analytical personality is even more introverted than my creative personality and probably appears quite cold and aloof to others.  "Robotic" would not be an inaccurate term to describe my analytical personality.

It may or may not be due to different lobes of the brain, but my theory is that when I use the functional but rarely accessed analytical parts of my brain, the fun-loving, intuitive, creative part of my brain goes somewhat dormant, and I think, feel and react differently than I do at other times.  I don't think I'm alone in this - it probably happens to others too, whether they're aware of it or not. It's possible that my introspective, contemplative meditation practice makes me more aware of these changes that I would be without the practice.

But anyway, my name doesn't change, I don't have a different or alternative history and memories, and it's not like there's a different ego-self living in my head, but there are at least two different sets of personality traits that can emerge depending on what my mind is doing otherwise.