What do we do while deciding if free will exists?

[The Grand Nudger]

The fact is that I'm completely immersed in the fairy tale that we call human existence--

-and yet you and I can have this conversation...we can express this doubt, we can both accept that it is not all as we see it....so no...judging by this conversation alone neither of us is so immersed, and immersion would not be any excuse for advancing a non-factual position -as- fact by brute force.

 and free will is no less valid in that fairy tale than anything else is. 

that which is valid is not always true.  

The reality of physics and the reality of what it's like to be human are very different things, no?

Doesn't seem so to me....any disparity we're likely to reference is circumscribed, explained, and in fact a description -of- the physics of our perceptions, and I would say...no disparity -at all-.  You experience your wife as a physical object, for example -despite being empty space- because you are not structured in a manner that allows you to pass through her.  Similarly, you experience the soil beneath your feet as a "solid" block - impossible to traverse simply..a nematodes experience of the same is vastly different...and in this example not due to a difference in stuff or structure..merely a difference in scale. If you were structured differently, or of a different scale, your experience would be a description of those things, that relationship, instead.

You and I perceive that which we are equipped to perceive, in the manner that our perceptions are capable of perceiving them......there's a reason you can;t read my mind..there's a reason you don't see ir..there's a reason you don't hear infrasound, and there's a reason that you can't actually detect temperature as an absolute.... Don't you think?