I watch a few videos on youtube saying that the time may be an illusion, what they mean by that? If time is an illusion, then why our brain knows when to sleep? and why the brain knows when to wake up (at the right time) And about the birds that agree to wake up at the same time every day? And why when we take melatonin, the brain regulates at the right time which we all should sleep? (between 9-10pm). I do not understand why they say "illusion", to me it seems VERY REAL.