Why is it easier to stay up late than to wake up early?
For many people, internal clock is naturally delayed, said neurologist Dr Yatin Sagvekar. This means biological drive to stay awake peaks later in evening. Neurotransmitter adenosine, which causes sleep pressure, declines when we stay awake late, said Dr Sagvekar. When people try to wake up early, balance between adenosine clearance and circadian alertness is disrupted, causing grogginess.