Why do you feel a sudden energy spike when you stay up late?

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At least short term I suddenly lose the sensation of sleepiness and become more energized when it’s been a few hours past when I should be in bed.

I’ve always wondered why that occurs but Googling only gives me articles about the effects of sleep deprivation

In: 7

Good question. Have you tried googling the natural peaks in cortisol levels that humans experience in a day? Cortisol is a natural ‘stress hormone’ your body uses to sustain activity in times of stress – ‘good’ or ‘bad’ kinds.* Additionally, adenosine levels build up continually through the day which contribute to a feeling of sleepiness by bedtime (although this is interrupted by caffeine which is why dosing with it can keep you awake), however aside from that there are natural variances/spikes in cortisol levels as well throughout the day, and inbetween them you might feel relatively tired as well (like the mid-afternoon slump). Like I say, have a google and see if that helps at all? Your sudden energy could be a natural cortisol spike. Re: adenosine and caffeine; caffrine also stays in your system for ages (it has a ‘half-life’ of about 5hrs I think – meaning that every 5hrs it’s concentration halves in your body. 150mg in a 7am coffee can mean 18.75mg still in your system at 10pm for example).

*This may be an inaccurate over-simplification so I’m hoping someone with knowledge can explain better than me!

You know how caffeine gives you a short energy boost then makes you more tired, right?

It’s because feeling of tiredness is caused by our body releasing melatonin until we decide to sleep. There are receptors in your brain that detect it, and if they interact with it they make you feel tired. Caffeine clogs those receptors making it impossible for them to detect anything, but melatonin is still produced cause we still are not sleeping, so when our bodies natural error correction mechanism gets rid of the caffeine you suddenly get hit by tiredness due to excess melatonin.

A kind of reverse thing happens in the situation that you are asking about.

Your body is producing melatonin making you tired cause you are past bed time. But you are still constantly working and being active like normal instead of sleeping as you should, so at some points your body starts to think that the melatonin in your brain isn’t there intentionally and is more akin to being an intruder like caffeine, so the same error correction mechanisms start to remove your own sleep hormone from those receptors, giving you an energy boost. It’s never stops sending out melatonin though, just the reception of it, so you suddenly become really sleepy after that boost ends.