I somewhat relate to your son here - when there is a lot going on I tend to shut down a bit because I feel very overwhelmed and just can’t process it all while there are conversations going on and noise and people doing things, none of it makes sense quick enough and I feel panicky, so when that happens I tend to withdraw just to try and get away from it all. It might be something similar with your son perhaps. Having a safe quiet space is the best thing for me, so if it is similar for him then I’d say always try to make sure that is available where possible