I found this via Google earlier this evening:
"If you drink milk long past the expiration date, you run the risk of developing food poisoning from unhealthy bacteria that might have grown in the milk. Food poisoning can be so mild you might not even realise you have it, but it can be severe in some cases. You might develop stomach cramps, nausea, diarrhoea or a fever. It can last for hours or days, and you might start to feel the effects of the bad milk within a couple hours of drinking it."
And so it was yesterday, a couple of hours after putting milk past its expiration date in my tea, I began to feel unwell. Over the course of the afternoon and evening, I developed stomach cramps, nausea, diarrhoea (I'm nothing if not honest) and a fever. Today has also been something of a "struggle" (if you know what I'm saying).
If only I had Googled 24 hours previously. Or been arsed to go to the shop.