You have been asked to see a 37-year-old female who has presented to A&E with retrosternal chest pain. During the history she reports that the pain is worse when she takes a deep breathes in and it came on suddenly a few hours ago. She has recently returned from Australia after travelling to see her sister. On examination you notice that she is tachycardic and hypoxic. A pleural rub is also present on auscultation. What is the most likely diagnosis, based on the history?