The Green Millennium by Fritz Leiber

As the elevator door closed behind Phil and he started the weary climb from twenty-eight to twenty-nine, he was already tormenting himself for having turned down Phoebe Filmer's invitation to have a drink in her room. When she had accosted him in the lobby, babbling about how he had rescued her at the Tan Jet, he had felt the last thing he wanted to be with was a human being. But now, with nothing separating him from the loneliness of his room but an echoing flight of stairs and an empty corridor, he suddenly realized that he needed human companionship above everything.

He remembered how boldly he had set forth just yesterday afternoon from his room to look at life and plunge into any adventure that came along. And as it happened he had seen so shockingly much of life and been buffeted by such vast oceans of adventure, that his brain still buzzed from it. At times during those incredible twenty-four hours, it had seemed to him that his whole character was changing, that he was becoming the daring yet sympathetic adventurer and lover he had always dreamed of being.