Even though the vast majority of my work was outside television, the amount of creation and inventing that went into the TV shows was non stop and, unknown to me, a great strain.

Meaning of the quote

Paul Daniels, a well-known British entertainer, is explaining that even though most of his work was not on TV, the amount of creativity and new ideas he had to constantly come up with for his TV shows was very tiring, even though he didn't realize it at the time.