To be fair though, they hadn't gone out drinking and then flying. They had drunk the night before and believed they had slept it off. I personally can't feel a pint of strong lager inside me, it takes 2 or 3 before I'm aware that I've drunk. So I do it by calculation that a can of strong lager is 3 units and you process a unit an hour.
So it's more than possible they took off feeling fine, believing they were fine, but unfortunately weren't fine.
It also seems similar to the very sad Cirrus loss over the channel on the weekend. Non imc pilots relying on auto-pilot to fly IMC