This is a classic dissociative bad trip. Salvia brings it about most often, and from among the psychedelics it seems that mushrooms are most prone to causing it (they always seemed the most dissociative of psychedelics to me). Myself, I've caught glimpses of it on shrooms and 5-MeO-DMT, even though my personal version of bad trip is a bit different.
People equate what you have experienced with concepts such as block-universe determinism (or their religious counterparts). Myself, I suspect the reason for this kind of trip is that as the psychedelic stimulates your mind, all your thoughts hit the 'ceiling' and become equal in intensity. In normal conditions, there is a hierarchy of reality; the present moment and the external world are the strongest (the most 'real') stimuli and the information from your memory and imagination is the weaker background (that is perceived as less real). When you take high doses of psychedelics, all your thoughts are pushed to the upper limits of intensity and your memory and imagination of the future become as 'real' as the present moment, causing you to see past, present and future simultaneously and equally solid and leading you to believe that the future is as set as the past and present. (I call this the God mind or 4D spacetime perception) This is an illusion, as the future you are seeing is your imagined future, you're not becoming precognitive.
Dissociatives also equalize reality and memory + imagination but at the bottom level rather than at the top.
I've also had similar problems integrating a 5-MeO-DMT trip, with the nausea when I thought about it and everything. The good news is that you can take the blue pill. If you do not take psychedelics again it will fade away from your memory and you will return to traditional reality. Plunging head first into reality and having fun, socializing and drinking alcohol also helps.
But the real benefit is if you can integrate this into your normal frame of reference. This psychedelic revelation seems at first fundamentally different from your previous perspective. But if you manage to integrate them, to find a larger frame of reference into which both fit, you can combine the benefits of both and use the psychedelic revelation to enhance your life. Even though they seem contradictory at first you can have your cake and eat it too.
You should stop seeing them as mutually incompatible realities, let them both into your mind and look for ways in which you can translate them into each other and melt them together. And you may find in the end that they are different perspectives on the same thing.
Also, it might be helpful if you also consider the problem rationally, from a philosophical pov. If you find a rational solution you can use it to facilitate your intuitive and emotional understanding. The rational mind is more controllable and you can use it as leverage on your 'soul'. In my opinion, the definition of free will has little to do with whether the universe is deterministic or not.
I think ultimately the dissociative experience can be very valuable when applied correctly. By showing you the ephemerity of life it may push you to really make the most out of your life and rise above the bullshit with which many people waste it.