shakespork:

Here’s what you’ll need to know!
Learn all about the wonders of the human body and add scientifically-accurate drama to your stories.

MALNOURISHMENT

• DEATH: average – 21 days (3 weeks), max ever recorded – 70 days (2.3 months)
• 6 HOURS: grouchiness and hunger due to lack of glucose.
• 24 HOURS – 48 HOURS: hunger very apparent; pains in stomach; body has entered ketosis and is using fatty acids as energy.
• 72 HOURS+: muscles begin to get broken down for energy.
• You will become: increasingly depressed, irritable, hysteric apathetic; decline in concentration, comprehension and judgement; social isolation and withdrawal; possible self-harm.
• If your character doesn’t eat for 5 consecutive days, they are at risk of Refeeding Syndrome. This is extremely dangerous and can be fatal.

recommended reading:

• The Minnesota Starvation Experiment
• Psychology of starvation based on the above experiment.

DEHYDRATION

• DEATH: average 3 days; some live 8 – 10 days
• for the calculations: TWV = total water volume in body; average adult loses 2.5 litres of water per day.
• Assuming that your character does not eat, drink or absorb any moisture.
• 9 HOURS/2% TWV: thirst, discomfort, dry skin, loss of appetite; 50% loss of performance for athletes; elevated body temperature, rapid heartbeat, fatigue, dizziness when standing, decreased fluid secretion (sweat, urination, tears, etc).
• 24 HOURS/6% TWV: sleepiness, severe headaches, nausea, tingling in limbs.
• 36 – 72 HOURS/ 6 – 15% TWV: no urination, seizures, muscle spasms, shriveled skin, fainting, vision dimming, delirium.
• 72 HOURS+/15% TWV+: Organ failure.

recommended reading:

• dehydration on the psychology wiki.

SLEEP DEPRIVATION

• DEATH: not known, but can stay awake for 11 days; max chronic sleep deprivation ever recorded (until death) – 6 months.
• NOTE: This does not mean you can stay awake for 6 months. It means you can survive that long with chronic sleep deprivation – going days without sleep and then sleeping once or twice.
• 24 HOURS: mental ability impairment of someone who has blood-alcohol content of 0.10%; everything is worse – emotional control, memory, attention, decision-making, hand-eye coordination.
• 36 HOURS: hormonal spikes everywhere; losing time; lack of motivation; head buzzing like you’re dehydrated.
• 48 HOURS: microsleep, regardless of what you’re doing (you fall asleep for 1-30 seconds and then become disorientated);
• 72 HOURS+: say goodbye to higher mental processes like decision-making and planning. Also, say good bye to saying goodbye because even simple conversations are hard.
• 80 HOURS+: … and hello, hallucinations!

recommended reading:

• this article of a soldier’s experience with sleep deprivation.
• Eleven Days Awake; The Experiment.