What actually happens if your baby drinks post-alcohol (significant amount, like hangover worthy type) breastmilk?

To answer your question - there is a fine line between knocking back one,two or even three glasses of wine and getting drunk and then feeding your baby. Drinking up to 3 glasses won't have much of an effect on your baby (though if possible it is advised to wait 2-3 hours before you nurse) If you are flat out drunk that's a diff story. First there is a chance that you could hurt baby because you are drunk, secondly, the alcohol levels might cause mild sedation in your baby.