I always found smiling to be a forced affair for me.
   I do it; and at this point in my life I can project feelings
   through the strange contortions of the facial muscles, the eyes,
   etc.

   But it's usually rather odd to me. I tend towards a plain face.
   No expression. I fight it because it's been culturally imbued
   into me, but my nature is generally somber. I fake it well for
   the cognitive benefit of others; people expect smiling and
   they're happier if i do it. I also exaggerate for entertainment.
   But by myself? Just a regular face.

   I don't see the old pictures as unhappy at all. I see them as
   neutral faces.   For example, a few months ago, I relaxed all of
   my facial muscles and took a picture. That's my neutral position
   face. I don't consciously allow my facial muscles to go neutral
   like; again, cultural training - but if I'm working or relaxed,
   I suspect I look like this.[1]ken-neutralface

References

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   1. http://icopiedyou.com/wp-content/uploads/2015/10/ken-neutralface.png