I'm formally assessed with selective mutism and ASD. I've had the condition my entire life but it is much more pronounced now in adulthood since I've had an autistic breakdown. My speech completely shuts off, physically and mentally. I don't know what to say, and nor do I have the energy or motivation to say anything.
Mine has always been more pronounced with my family than with strangers, in part because one is expected to share emotions with their family. I have severe alexithymia so I don't understand my emotions, I get stressed, and my speech shuts off like a light switch. In public I can usually mask and fake it enough to tolerate basic exchanges, but it's demanding as well.
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And in the end, the love you take is equal to the love you make.