Pattinson, 29, confessed he often gets "embarrassed" at the gym and still worries about his acting abilities.
"I'm definitely very confused. I spent basically my whole 20s having no idea what was going on. And I do feel now that I'm gaining a little bit of perspective," he continued.
He said he feels like "a fraud" and is in "turmoil" over a need to prove himself.
"I definitely feel like I need to prove something, and I'm not entirely sure what it is," he added.
Pattinson shot to fame after his appearance as Cedric Diggory in Harry Potter And The Goblet Of Fire before taking the lead role of Edward Cullen in the Twilight films.
He moved back to London shortly after getting engaged to 27-year-old singer FKA twigs six months into their relationship.
The pair started dating after the end of his romance with Twilight co-star Kristen Stewart.