It's a matter of opinion and belief on your entire view of life and your world. It seems like you're under the view that this physical world is the only real thing, and all else perceived is created by our physical pink slimy thing. Others think differently. You have to at least be able to understand their differing opinion a little bit, right? I can understand yours, but 'it's a dream ffs' is dismissive and not really saying much of anything. What is a dream? To be able to answer that, you'd have to understand the mind, which we don't yet. Until then, all we have are beliefs, hypotheses, and/or opinions.
As to the OP's challenge, as I think it's already been gone over here, altered states are a confirmed phenomena of the mind and there is no need to prove that they exist to you. What you think they are is up to you, but they are there, I can assure you.
Or they just don't care enough to jump through even the smallest of hoops for you, the random abrasive challenger to something they may or may not care if you even believe exists or not. That, or they're just filthy liars.
I didn't want that to come out as abrasive as it did, but I'm just going to put it out there that these are the type of responses you may get if that's the type of energy you're putting into the pot here, OP. In the words of Conan O'Brien, "keep cool, mah babiiies".