Why do I have to wake up every day?
A chemical that built up while you slept drains away, and a brain clock flips you back on.
Sleep is not an off switch, it is maintenance
Waking up feels like the default and sleep like the interruption, but biologically it is the other way around. The body schedules sleep on purpose to do work it cannot do while you are running: clearing metabolic waste, filing memories, resetting hormones.
Every hour you are awake, a molecule called adenosine accumulates in the brain. The fuller that tank, the heavier your eyelids. Sleep is the only thing that empties it, which is why you cannot simply will the tiredness away.
Two systems decide when you switch
Sleep and waking are governed by two clocks running at once: a pressure that builds with time awake, and a circadian rhythm tuned to roughly 24 hours by daylight.
Overnight, sleep drains the adenosine and the circadian clock swings toward day. As morning approaches, a pulse of the hormone cortisol pushes alertness up, and you surface, often a few minutes before the alarm.
Why it has to happen again tomorrow
You wake every day for the same reason you eat every day: the need refills as fast as you spend it. There is no version of rest deep enough to last a lifetime, only enough to carry you to the next morning.