Drug-induced mental states may be hard to describe, but people try pretty hard. Below are a few quotes from Erowid.org "experience reports" in which people describe not feeling free will. I don't see much of a common thread between them.

It is a very zen thing; everything seems so simple and just so. The beautiful, illusory nature of ego consciousness was just so obvious, so plain to see and easy to understand. In the absence of time, the paradox of free will and determinism vanishes. Life is a wonderful game, a grand, extraordinary drama and although we tend to get overly caught up in our roles, that's exactly what it's all about. The forgetting and the remembering, the getting lost and the coming home, over and over again.

I can’t remember what I else I tried, but every time everything would happen just the way it happened before, and I couldn’t change anything. It was like I (as God) was always one step ahead of me. Each time the universe was created, everything happened exactly the same, exactly the way it was supposed to happen.

My place in the universe is like that of a water molecule bouncing between sticks and boulders in a mountain stream. I don't know where we're going, I don't know why there's this force 'gravity' that pulls me and influences my motion, and I'm not sure I have any free will in choosing which boulder I will interact with, but for some reason, I don't really care. If this is what the universe is, then I will gladly partake.

The trip then became some sort of awful parody of my own existence, taking on a dark and demonic funhouse sort of feeling, where everything was distorted and mutated in some sort of horrifyingly comedic way. I looked at K and said 'dude, what the fuck?...' and pointed at K, then he pointed at P and P made a strange dismissive sort of gesture and then I said 'dude, what the fuck?...' and pointed at K and he pointed at P and, horrifyingly, the cycle continued. I found myself stuck in an incredibly long timeloop and I thought myself that, if I didn't play my part in the loop, it would end, but every time it came around to my turn to make my gesture and, thus, continue the loop, I would find myself pointing at K. I had somehow lost my free will it was horrifying. I truly believed I would be stuck in this loop eternally, but something strange happened: K's third eye opened up and he bent down and vomited out his consciousness.

I got up and paced around for a while, feeling as if I were outside of my body, yet still able to direct it, almost unconsciously. It was as if my free will was somehow usurped, yet I was still more or less in control, it is hard to describe that feeling.