This might be a tangent. I attribute my bombing a big4 interview in 2014 to restless and sleepless night the day before the interview (it was a very senior dev position and the role and responsibility described by the recruiter made me super excited. Actually, the whole week had been pretty much sleepless nights) which 'disabled' my hunger, and the lethal combination of sleep deprivation and overnight fasting manifested itself and I literally saw myself failing at things I shouldn't have but I could do nothing about it. It was a 9 am meeting and I was in a cold hall which added to the misery. I was groggy, about as articulate as a drunken child and utterly failed to benefit from the generous hints the interviewer was giving me. I felt sorry for him TBH. It was the company that had contacted me and I felt pretty bad for the recruiter as well for having fared so miserably. The biggest takeaway from this experience was to get sufficient sleep the night before important events. And to bloody eat breakfast.

So, are you sure your failure is not due to external elements like mine (which was one off fyi)?