I think people are mistaking the idea of struggling on with a hangover, with being so hungover you are incapable of looking after a child. In my experience the difference is how motivated the adult is rather than the exact symptoms.
Some people are motivated to make sure the child is ok, and some people don't give a shit as they're too busy whining/ vomiting/ still drunk etc.
The two situations are sadly, very different.
Taking the alcohol out of the equations, these two examples work quite well (sadly):
E.g. 1 I was still being a good parent and prioritising DS wellbeing when I was very ill but had no one else to watch DS... by very ill I mean being blue lighted to hospital that night. Sometimes we think this is the norm as we'd all prioritise our children if we were even vaguely conscious. It's what we do.
Eg 2 poor DS's father was so selfish he couldn't see what the matter was with him being 'so tired' that he fell asleep when in charge of his poorly baby, it had only been 45 mins on his own as I'd been up all night with DS, not Mr- I'm so tired & selfish wanker. He couldn't even rouse himself as the poor diddums was SO tired when I came in and discovered DS floppy and unresponsive and lying unclothed on the floor, and his fucking father snuggled up on the sofa having a lovely nap. I ran carrying him out of the house to hospital, with him swearing behind me as I'd dared disturb his sleep. Didn't even phone me for almost 24 hrs, excuse being he needed some sleep and besides, DS was with me so would be fine... fine, though the last time he saw his son he was hardly breathing and I was screaming about hospitals... where the fuck did he think we were?! Well, in hospital with suspected (eventually ruled out thank god) meningitis.
Tossed.