Answer: it arises from hidden impulses at the unconscious level
Explanation: According to the Fued and unconscious mind theory, hidden impulse is the secret urge that stays in the mind in unconscious stage. Impulse rises at sudden movement from the unconscious mind. The contains several thoughts, emotions etc that are mostly unpleasant without the awareness of conscious mind.
The situation of Sandra's reaction in the question describes about hidden impulse she had towards her cube-mate's annoying activities. She had a thought of violent outburst towards him which was raised by the unconscious mind .