Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Prinzmetal's variant angina ?
    ### Response:
    Prinzmetal's variant angina is characterized by recurrent episodes of chest pain that occur while an individual is at rest. This condition is a form of unstable angina because the episodes do not occur in a predictable pattern. Prinzmetal's variant angina may occur spontaneously, or it may be caused by exposure to cold, emotional stress, alcohol withdrawal, or vasoconstricting medications.
    