A better way of articulating 'ataractically candid'

I'm trying to convey the sense of a rare moment of tranquility in the mind of a confused, flawed and tormented character.

This is the most ataractically candid thing I've ever written.

This occurs at the end of a sincere, formal letter to a business partner asking for forgiveness.

I want to convey that the candour comes from the rare state of ataraxia the character is feeling at the time. Rare because they suffer from extreme bipolar disorder, and they are out of their mind more often than not.

As I suggested in my answer to your previous question, I like serenely, which to me suggests a haven after a tempestuous journey—or at least a temporary respite from the tempest.

But again, serenely candid suggests the manner in which the candour is expressed rather than the source of the candour.

Perhaps:

This is the most candid thing I’ve ever lucidly written.