> What happens after we die? You stop being.
You don't know that of course, and have no way of knowing that. Although I'll agree that from a modern, rationalist point of view that's the default reasonable assumption.
> What is consciousness? A physical process happening in your brain.
And same goes for that one; the brain clearly relates to consciousness, but you can't be sure it produces it. Maybe it receives it somehow; maybe it's even more complex than that. I'd even go as far to say that if we were to create a black box AGI tomorrow, the question would still not be solved: the only thing you'd have proven is that a specific arrangement of matter appears to result in consciousness, nothing more.
Moreover, reality itself happens - in a very concrete way - in your head, not outside of it. Plato's cave and all that (or for a more technically oriented one, the brain-in-a-jar idea). Your point of view is rational in the extreme, but also extremely reductive. I don't think one should be so quick to reject deeper - and, dare I say, spiritual - ways of considering our universe.