Katherine filed the declaration as part of her bid to obtain co-guardianship over Prince, Paris, and Blanket.

In the docs, Katherine claims she was scheduled to go on a road trip to New Mexico to watch her sons in concert -- but on July 14th, an unnamed doctor showed up to her house and told her it was better for her to take a plane instead.

Katherine says she obliged -- believing the doctor was under the orders of her longtime physician -- but when she got off the plane ... she found herself in Tucson, where she had been set up at a luxury resort.

According to her lawyer, "Her children took her to a spa ... because she had high blood pressure."

When she got to the resort, Katherine says her phone and iPad were taken away -- and her in-room telephone was disconnected. She says her TV was also shut off.

When Katherine asked about the grandchildren, she was told "they were fine" and there was nothing to worry about. She says she did NOT know she had been reported missing and her grandkids were freaking out.

Katherine says, "At the time, I trusted the people I was with to be honest with me."

The declaration flies completely in the face of the statements Katherine previously made in an interview with ABC News, when she called her sudden absence last month a "short vacation."