Wretching and gagging could be because of condition as simple as acid peptic disease
and he'll do better with antacids. But it can be because of severe causes like gastric upset due to autonomous nervous failure as he's having diabetes
for a long time. If not verbal, can't you manage to get him write his symptoms, feelings on a piece of paper? That would certainly help you understand whether you should care to take him to show a doctor nearby or if you can treat him with OTC antacids yourself. best luck.