Hi Kira, In the USA, sometimes people say he / she "flipped a switch", but it's not a perfect translation because it usually implies that somebody said or did something very rude after. Also, I'm not sure of its use outside of America. There are many words in English and Russian that don't translate easily. P.S. nervous in English isn't used to express annoyance or irritation like in Russian. To be nervous means to be worried about something like an exam for example!

Thank you for trying to help me! It generally means "get so angry and nervous, get almost psycho because of that")

Hmm - google doesn't give any translation. Some online dictionaries suggest 'psych'.