Autistic son having “funny turns”

Looking to see if this is something familiar to others. 

My son is autistic and is 12. Twice in the last week he has had a weird thing happen where he says he feels like there’s a giant gobstopper in his mouth and he finds it hard to breathe and then there’s loads of saliva which he has to spit out. 

I don’t know if it’s a stress thing - he’s about to start high school. Though he says he doesn’t feel stressed. It happened once when shopping for school shoes, and once after a hair cut (which he does find stressful for lots of reasons) 

Has anyone had an experience of something similar?

just keeping an eye on it just now.