Supposedly carbohydrates are a precursor to serotonin, so getting sleepy from carbs could be expected. The neuroscientist Andrew Huberman talks about this in his podcast, eating low carb during the day can maintain alertness, while eating carbs at night are useful to prepare for sleep.

A heavy portion of carbohydrates will raise and lower your blood sugar levels. The crash is the tiredness. I would nearly fall asleep at my desk after lunch if I had pasta, and it took some time to make the connection.

It does not do that for me. As in, I don't get tired after eating them.

So I think, it is quite likely that it does affect other people differently. And it makes sense for them to cut that stuff out while I don't have to.

There are different kinds of intolerance. Some people have mild allergies to gluten, which is very different from celiac disease.

Why do you think this has anything to do with gluten? Is there perhaps another substance in bread and pasta that is known to contribute to sleepiness after eating?

Good point. I don’t really know if it is gluten. I hadn’t thought of that!