Why are people always tired during the day?

Answer 1

In some cases the person is not tired; drowsy.

Keep in mind that your body induces a self-paralysis to prevent injury during sleep.

You're being freed from that paralysis when you wake up.

Makes you're kind of stiff, tired, drowsy, etc.

Also, your metabolism slows down during dormancy.

Waking up and doing stuff while your body's still asleep leaves you with a lack of energy being produced, leaving you feeling tired. (For just a bit)

(BTW, Sleepwalking is a disorder where this paralysis doesn't correctly shut down the brain's motor skills, and the body remains at the whim of an unconscious brain.)

A major reason why many people wake up tired is that they suffer from sleep disturbances that can include sleep that is interrupted many times during the night, inability to fall asleep for hours, waking up very early and not being able to get back to sleep, profound sleep disorders that prevent any restful sleep at all, fibromyalgia that induces pain during the night, other pain disorders, insomnia caused by stress, medication and anxiety, and sleep apnea induced by breathing interruptions.

An evaluation at a sleep study clinic may help determine the reason.

Answer 2

The biggest reason is not getting enough sleep at night.