What about “UnderSensitivity?

It might be noted that Temple Grandin now appreciates intense squeezing, hence the “cattle crush” she created for herself, quite at odds with her hyper sense of touch. So the question also arises about UnderSensitivity. (And UnderSensitivity may be the case with your Child.)

Given Temple’s concurrent oversensitivity, my impression is her brain can “turn down the volume” of that sensitivity, to make it more bearable. (There is the possibility that the continual overstimulus might “burn that sense out” somewhat, needing stronger-than-normal inputs to reawaken it. But I tend to think it is more of a self-controlled mechanism.)

There is further evidence the “turn down” mechanism, which probably fluctuates depending on how much the person jumps between the Real and Own World. For example Donna Williams 1998: “Sometimes people would have to repeat a sentence several times for me, as I would hear it in bits… sometimes left me with an unintelligible message… like when someone plays around with the volume switch on the TV” (Tony Attwood: “The Complete Guide to Asperger’s Syndrome” p 277.)

Since under or over sensitivity would still appear to be part of the same condition, ultimately the issue is not highly important
if the result of Withdrawal is the same. (It is said that more-autistic children can be highly resistant to pain, and I have seen it for myself with a 4 year old girl with a broken collarbone: her parents were unaware of it for some weeks. We know that some humans have deliberately cultivated the ability to “turn down the pain volume” when required, so my instinctive impression is the more autistic person has developed a similar ability, rather than the notion that Sense has “burned out”.)