When a person is first faced with the "threat" of nihilism, they seem to always feel great anxiety. The world around them seems suddenly foreign and ambivalent (or perhaps even malignant). They may feel disconnected and isolated from society, or sense their life is kind of exile.
If the person doesn't manage of overcome this initial angst by compartmentalizing or some other method, then they may feel despair and hopelessness. Their dreams, their impressions, their fantasies of what reality is like have been torn down. There seems to be no way to recover.
A human being cannot exist in an extended period of anxiety, though. Sleep may be the escape for some, and for others, drugs or other distractions are a way to ease the anxiety. But ultimately the anxiety does not permanently pass. It's physically exhausting to feel anxiety of any type for an extended period of time, and depressing to believe that the source of one's anxiety will not pass.
Hence why I believe apathy is the final expression of nihilism. For to act upon nihilism is to attempt to make meaning in a meaningless universe. To construct or destroy is to try to take control over a world outside of your control. It's to not accept that the world is what it is. To be apathetic is to neither deny the reality of nihilism nor embrace it - for it's useless to fight nihilism, but equally uncomfortable to embrace it.