I did that in grade school
At the verbal English exam i was given a lesser score ( 11 out of 13 ) CUZ i spoke American not English,,,,, i was like WTF.
And the guy sitting next to me he got a 03, which was also a outrage CUZ he was easy able to say " hello my name is Bendt" so for that he should at least have gotten a 5
In chemistry in 10 grade ( where i stopped school in the middle of the year to get a job ) well having not studied anything the teachers sent me letters about studying, i had worked myself up so bad.
So i picked a random topic, which was acids / bases and the periodic table, something i could easy have gotten a 13 in, but due to nerves about picking anything else i only got a 10,,,,, i was so worked up i could not draw a line on the board it became a dotted line as i was shaking so much.
I really suck in exam or competition, you can easy deduct 25% from my average performance in situations like that.
And it do not matter how good i am at something, add the element of competition and i will not perform as good as i could.