I’ve met people who are doom-and-gloom because they’re near the end of the PhD. Typically this is because their viva is coming up, though there can be a host of reasons – general concern about examiners, wondering about corrections, worries about the future, and so on. It is worth spending effort to work on these issues. Figure out what’s troubling you, start to think about what you could do to work it out.
It’s also worth finding out more about general viva experiences and expectations. A lot gets said about the viva, not all of it good, not all of it true. Generally? The viva’s an interesting discussion about your work.
If you can find enough true stories of the viva, then perhaps other concerns might melt away.