How can inkcap mushrooms give you the worst hangover?

I am a mushroom hunter and have only found these once on Horsell Common.

Yes, the same common mentioned in "war of the worlds".

I didnt manage to eat them as I did not know at the time they only last for 12-14 hours and then turn into a black ink mush.

They are supposed to be a great tasting mushroom, especially lovely in a creamy sauce.

You can make ink out of them too