Technically speaking, everybodies personality is made up of a combination of other peoples personalities. So it's no surprise that you feel like you're mimicking somebody else depending on the situation. I think everybody does this. The person you know at work, isn't the same person hitting the clubs at the weekend. We all put on different persona's that we feel are suitable for a particular situation. Although, i'd say we're probably considerably worse at choosing the correct persona to put on in any given situation.
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Prof-Diagnosed: Aspergers Syndrome (I still call it that!), Dyspraxia, Dysgraphia
Self-diagnosed: ADHD-PI, Social Anxiety, Depression
Treatment: 5-HTP, Ginkgo Biloba, Omega-3, Pro-Biotics, Multi Vitamin, Magnesium