Nausea, Jean Paul Sartre
Ah existentialism, you tricky concept! As I understand it:
Existentialism = existence precedes essence = human beings have the freedom to do whatever they want in order to create their own essence or purpose = massive responsibility for your actions = anxiousness = EITHER denying the responisbility and in turn the freedom, OR becoming inspired by endless possibilities.
Nausea is pretty much a fictional version of Existentialism and Humanism, but without obvious theory. It takes the form of Antoine Roquentin’s journal, which he keeps methodically to detail his day to day observations. Roquentin doesn’t have a lot to do, therefore a lot of opportunity to sit around philosophising. Although this is technically an easy read, it is nowhere near a page turner! Pretty bleak, although interesting.
I’d recommend reading Existentialism and Humanism first to get the basics, as otherwise reading Nausea will probably feel like you have interrupted a story half way through the telling.