Why You Pick Fights When You’re Tired
Part three in this year's sleep series
We’ve covered sleep pressure – the biological drive that builds throughout the day and makes you actually want to sleep. We’ve talked about gut health, adenosine, caffeine, and why “just relax” doesn’t work if you haven’t built enough pressure to fall asleep in the first place.
What we’ve not come onto yet are the real dangers of not sleeping.
Not just grogginess. Not just needing more coffee.
The stuff that quietly wrecks your relationships, your food choices, your digestion, your immune system, and your ability to have a reasonable conversation without getting defensive.
In my conversation with Nicole Askwith Williams last week, we talked about how many arguments start because we feel exposed and cannot admit we do not know something. And the week before that Jon Xue Zhang said a line that stuck with me:
“Don’t trust your emotions after 9pm.”
When you’re sleep deprived, your emotional brakes fail first.
And the scary part is, a lot of us aren’t just sleepwalking into it, many of us actually boast about how little sleep we think we need.
Sleep deprivation feels like mild intoxication
After around 17 hours awake, cognitive impairment can resemble being legally intoxicated. Reaction times slow. Judgment wobbles. Emotional reactivity climbs.
You would not trust yourself to negotiate a conflict after a few drinks.
But people do it everyday when they’re under-slept.
This shows up as:
Defensiveness
You misread tone. Neutral comments feel like threats. Curiosity turns into confrontation.
Impulsivity
You say things you would normally filter. You press send on messages that should have stayed drafts.
Poor decisions
You reach for quick comfort over long-term benefit, not because you’re weak or a bad person, but because your regulatory systems are offline.
Your body takes the hit too
This isn’t just psychological.
Sleep loss disrupts glucose regulation, increases hunger hormones, and reduces insulin sensitivity. You feel hungrier and crave–ier and store calories more easily. Digestion becomes less efficient. Bloating and reflux are more common. Water retention increases.
Inflammation rises. Immune response weakens. Pain sensitivity increases.
In other words, poor sleep makes your body feel stressed, puffy, wired, and tired at the same time.
The things that quietly ruin sleep quality
You can be in bed for eight hours and still wake up physiologically under-recovered.
Alcohol
Alcohol sedates you, but sedation is not sleep. It fragments sleep, suppresses REM, and increases wakefulness later in the night. Even moderate intake reduces emotional processing overnight and worsens next-day mood and cognition.
None is better than some here.
Late meals
Digestion raises body temperature and keeps your system active when it should be powering down. Late eating is linked to lighter, more fragmented sleep and poorer glucose control the next day.
A two to three hour gap between your last meal and bed helps.
Caffeine late in the day
Caffeine blocks adenosine, masking sleep pressure. You may fall asleep, but sleep depth suffers. Then you wake unrefreshed and reach for more caffeine, locking in the cycle.
And let’s have an honorary shout out to later day exercise: while some people can hang with it, many people find particularly intense training within three-four hours of bedtime to be counter-productive for restful sleep.
Willpower is a sleep-dependent resource
When you’re sleep deprived, the prefrontal cortex struggles. This is the part of your brain responsible for planning, impulse control, and emotional regulation.
So:
You eat for energy, not nourishment.
You snap faster.
You struggle to focus.
You avoid difficult conversations.
You create conflict you would normally defuse.
You think the problem is your personality, your discipline, or the other person.
If any of the above chimes with you, then…
reframe sleep as the start of your day rather than the end of it.
Most people treat sleep as leftover time. Something that happens after everything else.
Which is fine if you’re breezing through work, life and relationships.
But if you’re not, try and think about sleep as the start of tomorrow.
It determines your patience, your appetite regulation, your emotional steadiness, your cognitive clarity, and your resilience to stress.
Cut sleep, and you don’t just lose rest. You lose access to the version of yourself you’re trying to be.
The unsexy fixes that can make the biggest differenes
Not supplements. Not trackers. Not expensive gadgets.
Cooler nights
Your core temperature must drop to initiate deep sleep. A cool, dark room helps (aim for 16-19 degrees Celsius).
Regular wake time
Your circadian rhythm anchors to wake time more than bedtime. Consistency here builds stronger sleep pressure.
Earlier eating
Finish meals a few hours before bed so digestion does not compete with recovery.
Earlier hydration
Drink through the day, taper at night to avoid sleep fragmentation.
These are not glamorous. They are biological.
The bigger picture
Sleep pressure explained why you can’t fall asleep. This is about what happens when you don’t sleep well – and how to fix it.
You’re not necessarily lazy or not weak-willed. You’re not inherently bad at relationships or food choices or having difficult conversations.
You’re just running on a system that hasn’t been allowed to reset properly.
And when Nicole and I chat “how many arguments have we started because we didn’t know something and weren’t comfortable admitting it,” I think the real question is: how many of those arguments happened because we were too tired to handle the discomfort in the first place?
Jon was right. Don’t trust your emotions after 9pm. But also: don’t trust them when you’re sleep-deprived. Which, for a lot of us, is most of the time.
Fix your sleep. The rest’ll get (so much) easier.
Previous sleep pieces
Part 1: The more you try, the less it happens?
Part 2: Sleep pressure, gut health, fibre and un/helpful diagnoses
Thank you all so much for the support and feedback on the sleep series so far and last week’s episode with Nicole:
This week, Niell’s back to chat ego, injury, recovery and identity, and I can’t wait for yas to check it out.
And that’s it from me!
Much love, and I’ll see yas in the next one
J x
References & Further Reading
Alcohol and sleep quality:
Ebrahim, I.O., et al. (2013). “Alcohol and sleep I: effects on normal sleep.” Alcoholism: Clinical and Experimental Research, 37(4), 539-549.
Roehrs, T., & Roth, T. (2001). “Sleep, sleepiness, and alcohol use.” Alcohol Research & Health, 25(2), 101-109.
Sleep deprivation and decision-making:
Killgore, W.D.S., et al. (2006). “The effects of 53 hours of sleep deprivation on moral judgment.” Sleep, 29(3), 345-352.
Harrison, Y., & Horne, J.A. (2000). “The impact of sleep deprivation on decision making: a review.” Journal of Experimental Psychology: Applied, 6(3), 236-249.
Sleep and emotional regulation:
Yoo, S.S., et al. (2007). “The human emotional brain without sleep – a prefrontal amygdala disconnect.” Current Biology, 17(20), R877-R878.
Walker, M.P., & van der Helm, E. (2009). “Overnight therapy? The role of sleep in emotional brain processing.” Psychological Bulletin, 135(5), 731-748.
Circadian rhythm and sleep timing:
Czeisler, C.A., et al. (1999). “Stability, precision, and near-24-hour period of the human circadian pacemaker.” Science, 284(5423), 2177-2181.
Food timing and sleep:
St-Onge, M.P., et al. (2016). “Fiber and saturated fat are associated with sleep arousals and slow wave sleep.” Journal of Clinical Sleep Medicine, 12(1), 19-24.