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This afternoon, I'd drunk two and half cups of coffe that day, and I was slumping at 3pm.

I drunk another half cup of coffee, and that did help.

But then when I left work, at 7pm, I was totally wired.

Why is that I have all that energy and enthusiasm then, and not at the 3pm mark?

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up vote 3 down vote accepted

Your level of alertness is determined by more factors than your caffeine intake. What's known as the nap zone occurs around 3PM and affects some individuals more than others. Some scientists think that a long sleep at night and a short nap during the midday represent human sleep behavior at its most natural.

It may be that you're consuming a lot of caffeine. Extensive coffee drinking will increase your caffeine tolerance and requires you to increase your consumption to achieve the desired effect.

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The reason you feel "wired" at 7pm might be that (relatedly to your previous similar question) blood cortisol levels have another spike between 5:30 and 6:30 PM. I'd imagine this could be as late as 7PM depending on your lifestyle (time you get up etc.). So on top of your cumulative blood caffeine levels from the day, you'll feel quite alert!

I also find the physical act of getting up to leave work wakes me up - standing up from my desk, walking (getting blood pumping and delivering oxygen), going outside in the remaining sun.

And simply changing your focus from something you've been concentrating on for a while will help.

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