"I confess -- yes, I am afraid for my life. Because I don't know what will happen to me tonight. What the butchers of the Mordovia prison service will decide to do to me," she said in a letter passed to media by her former defence lawyer Violetta Volkova.
Her latest handwritten letter, scans of which were published by the New Times opposition magazine, is dated yesterday.
"It's not just that she is not in a condition to hunger strike; she is killing herself with it," she said.
"If you met Nadya on the street now, you would probably never recognise her."
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Tolokonnikova is serving a two-year sentence in the central Russian region for her punk protest group's performance in a Moscow church criticising President Vladimir Putin.
The 23-year-old last month went on hunger strike demanding a transfer to another colony. She released a letter detailing 17-hour days in a sewing workshop and a veiled death threat from the deputy prison governor.
She resumed the hunger strike today after returning to her penal colony Number 14 in the region dotted with former Gulag camps.
Yesterday afternoon, the prison service announced it would transfer Tolokonnikova to another colony.
Her husband Pyotr Verzilov wrote on Twitter today that Tolokonnikova was still on hunger strike and would continue "until the prison service's decision to move her is carried out".
Tolokonnikova and fellow Pussy Riot member Maria Alyokhina are due to be released in March next year. Both have young children. Each has had two requests for parole turned down.
He sent AFP a letter signed by Tolokonnikova and dated today formally refusing Volkova's services and saying she suspected her of "personal links to the prison administration".