This happens to me sometimes, especially after a meal which is very large or has a lot of fat in it (e.g. a good Indian curry banquet). (and probably if I am stressed as well) I can get hot and sweaty, faint and nauseous. Once after I ate a full meal after an exhausting day of hiking, I got a fit of uncontrollable shivering. Very scary - I thought I was going to die. I think it's best to eat small meals often, than large ones infrequently.
I too sometimes feel a social pressure to try and finish a restaurant meal. Thank goodness we don't have US-sized portions here, but at least in the US it's more usual to ask for the leftovers to take home, whereas in the UK a lot of places aren't used to such requests, so I feel bad at leaving leftovers which will just be thrown away.
But that is what I do. I will not eat more after I feel full. My friends tease me for having "a stomach the size of a pea" but that's how it is. They don't know that if I try to eat as much as them, I get stomach cramps and diarrhea when I get home.
Min
P.S. This is probably TMI, but if my bowels need emptying (as they euphemistically put it), then I am extra prone to anxiety. (This might be because the association works both ways - anxiety makes you want to evacuate your bowels, therefore if you need to evacuate your bowels maybe that triggers the association with anxiety). Indeed if I have a gyppy tummy due to a bug, I think the dodgy tummy feeling feeds back to convince me I must have anxiety, and I start feeling mentally queasy too.
P.P.S. I swear by peptobismol too. I like it now they make it in tablet form so I can always carry some in my handbag.
P.P.P.S. You could try asking for a child portion or have a starter as main course. Or ask for 'no fries' or whatever. Failing that, as I said, just get used to the teasing. Or go out with one of those useful people (usually, but not always, a male student) who has not much money and a bottomless stomach and will gladly finish off your meal for you. Then you get a clean plate, a grateful friend, and no horrible fullness. Very satisfactory reciprocol arrangement.