Below is an instruction from Human. Write a response.
    ### Instruction:
    What are the symptoms of Polycythemia Vera ?
    ### Response:
    Symptoms of polycythemia vera include headaches and a feeling of fullness below the ribs on the left side. Polycythemia vera often does not cause early signs or symptoms. It may be found during a routine blood test. Signs and symptoms may occur as the number of blood cells increases.
    