As Per the Major Upanishads, there are four stages of human consciousness called Jagrit, Svapna, Sushupti, and Turiya. These conditions are equated with the word ‘OM’ so that when someone encompasses the four stages becomes equivalent with OM i.e. Brahman.
We the beings on Earth perceive the objects of the senses through the same methods. It is through the action of neurons in the body. In Junior School Level, everyone has heard about stuff named Response to the Stimulus. It is the ideal condition for functioning the consciousness when a person wakes up. Now, whenever someone touches you, the skin sends a signal to the brain and sends feedback that you have to react to that touch. If the fire touches your hand, your consciousness m akes you remove the hand instantly. The same thing happens for all the objects you sense through the sense organs
The response to a stimulus for all the senses makes you perceive reality. This is called Jagrit Stage. In the Dream Stage, the responses may be the same but perceiving reality differs. In the dream, you might see yourself inside the sea, but when you wake up you realize you just touched the glass of water, or maybe you did pee while sleeping during childhood, or maybe the glass of water fell down accidentally.