There are altered states of consciousness that occur naturally and don't lead to a sense of euphoria. Sleep paralysis for example. It happened to me once and it made me see things differently, nothing religious or mystical, just an enhanced perspective.
To give an example, during my episode I had what is usually described as an out-of-body experience. I felt myself walking around my bedroom as if I were awake, only to find out that my body never left the bed. Now if the sense of being "out of the body" is an illusion, how can we be sure that being "in the body" is not just the same illusion? (I'm tempted to think we are not anywhere and that space itself is the illusion, but that is beside the point)
One can easily arrive at the same insight (i.e. being in the body is just an illusion) without actually experiencing it. Of course, if you have such an experience and you get knowledge or inspiration from it, so much the better. But to say that theorizing about consciousness is a waste of time if you haven't experienced altered states is myopic.
To give an example, during my episode I had what is usually described as an out-of-body experience. I felt myself walking around my bedroom as if I were awake, only to find out that my body never left the bed. Now if the sense of being "out of the body" is an illusion, how can we be sure that being "in the body" is not just the same illusion? (I'm tempted to think we are not anywhere and that space itself is the illusion, but that is beside the point)