розгубитися

To lose one's head; to be at a loss, to be disconcerted (embarrassed); to lose countenance

розгубитися від несподіванки — to be taken aback

не розгубитися — to keep one's head

я зовсім розгубився — I was embarrassed, I lost my head; розм. I went all to pieces, I was at a loss, I did not know whether I was standing on my head or on my heels