In the story "Paul's case," why is paul irritated

In the story "Paul's Case," Paul is irritated because his real life is so different from his dream.

After the concert, he began following one of the singers, and imagining she asked him to go with her to her room. He started living in that moment for a while, until he realized it was just a dream, and that he was standing in the rain in front of a hotel, not having been invited to join her.