The consciousness is often a product of its environment. An "idea" or perception doesnt exist unless it is able to be percieved and understood by the subject through stimuli.
laymans example: the idea of being suicidal is incomprehensible by person Y. It cannot be comprehended by person Y because said person has lived a prosperous, joyful life. He cannot possibly understand why someone would attempt suicide. Therefore in person Y's mind, such feelings do not exist.
Unless person Y has been in person X's shoes, experienced every level and kind of stimuli person X has experienced throughout life up to this point, he cannot understand why person x has developed to this point. However, to person X suicide is a believable reality that has come to pass due to unfortunate circumstance.
Moving forward, Since our consciousness is under the influence of [this] reality. we often cannot understand nor perceive anything else. Because our tendancy is to submit to a physical reality, due to physical stimuli.
Now, with this being established. How can you say nothing exists outside a physical reality, when all you know is physical stimuli?