Why is the narrator writing in secret?

The narrator has been prescribed a rest cure and is prohibited from exciting herself as she is diagnosed with a 'nervous condition' which nowadays would be identified as post natal depression.

Gilman based the story on her own experiences and the mental frustration which tortured her as a writer and intellectual condemned to inaction. In the story, the narrator hides her journal as she knows it is against her husband and doctor's wishes-

'There comes John, and I must put this away,--he hates to have me write a word.'