Get resting heart rate. Drink milk. Wait 20 minutes. If heart rate has risen by more than 10 beats per minute, then there's an allergy.
Mine went down. Of course, I wasn't resting that long. I think I might wait until this weekend to do it, when I can take my heart rate just after getting out of bed, drink some milk, then lie back down for 20 minutes. We'll see.
Of course, if after 20 minutes of rest, my heart rate is only 62 beats per minute, I'm probably not having an allergic reaction to the skim milk I drank. I'm not physically fit enough to have a heart rate much lower than that. So, hey, maybe I can safely drink skim milk (well, allergy-wise, anyway. There's still the whole lactose intolerance thing). So maybe I'll also try yogurt and cheese, separately, to see what I can more safely eat. Hmm, I wonder if this means I can go ahead and have baked things with milk in them on occasion. That would be good.