Perception of predeterminism
Feelings of predeterminism can be defined as the sudden perspective or feeling that all events, including human actions, are established or decided in advance by prior causes.
This is an effect which can become spontaneously triggered and felt through a distinct change in thought processes. In terms of how it feels, it can be described as the assumption that ones internal narrative possesses "free will" becoming revealed as entirely illusory.
The revelation is not a result of cognitive insight leading one onto a realization but occurs through a forced and often sudden change in perspective. This creates the undeniable sensation that ones personal choices, physical actions, current situational perspective, and the very subject matter of their thought stream have always been completely predetermined by prior causes and are therefore outside of conscious control. Instead of feeling as if they are dictated by freewill, ones thoughts and decision making processes become suddenly felt as a vast and complex set of internally stored, instantly decided, pre-programmed, and completely autonomous mechanistic responses to perceived sensory input.
Once the offset of the experience begins to take its toll the user will return to feelings of freedom and independence. They may however retain information and realizations regarding their insights into the nature of freewill long after the experience itself.