I don't think it's your diet that is causing this. I am also suffering from what you seem to be (I also have headaches, muscle cramps, extreme tiredness).
My diet is relatively healthy, I do have a bit of junk food every now and again, but I am getting everything I need from what I eat.
But for some reason I'm not able to think like I used to. For example, if someone told me eight months ago that I needed to remind them of something that night, I would easily - now I cant remember what I, or anyone, have just said. It is very had to describe, but it like I know the words I have just said, but for some reason the words cant come out of my mouth - like the signal from my brain to my mouth isn't working, or something is literately changing how I just saw (and spoke) in that moment.
I also have moments when my thinking slows down, and it seems like my thinking is in some slow-motion movie scene - I'm not sure if it's because of all the people around me, like you have described, but it definitely slows.
Do you think that what I have can be the same as you? If so, what could help with this?
PS. I'm in college at the moment and trying to learn how to drive but I my thinking affects my learning a lot.