Does anyone else experience these kind of self-doubts? 

Almost every time I have an appointment with my psych nurse and we discuss about my hallucinations and paranoia I think in my head "am I really experiencing things like this? Is this really happening or am I imagining everything and just telling lies? There's no way I would think that (for example) trees are staring at me I'm a clever highly educated person" (like it would even make a difference, it doesn't).

It's really controversial. While I tell about my symptoms I think stuff like that in my head. I'm questioning my own symptoms and experiences but in the end I KNOW I'm experiencing them. For example why would I close the curtains in my room if I wasn't afraid of trees watching me. But while I talk about them I feel kind of ridiculous and like "this can't be happening to ME.
 Is this normal?