Everything in Graveyard Keeper 2 is paid for in energy, and the game starts you with four of it. Not four percent: four points out of a maximum of ninety, which is about two swings at a tree.
Energy is the real currency of the early game, and the loop that refills it is never explained. It runs through food, through sleep, and through a number that quietly shrinks the tank itself.
Your maximum is a hundred minus your insanity
The bar is not a fixed size. Your ceiling is a hundred less whatever your insanity currently reads, and since you begin the game at ten insanity, you begin with a ninety point tank rather than a hundred.
That is the whole relationship between the two meters, and it runs one way. Insanity does nothing else to you: it does not kill you, it does not slow you down, it just takes the top off the bar so there is less room to refill into.
Nothing in the game punishes a high insanity reading except the ceiling it imposes. At eighty, which is the cap, you are working out of a twenty point tank and every meal is mostly wasted because it fills a bar that has nowhere to go.
Seventy nine things restore energy, and some of them cost you sanity
Almost anything edible works. Seventy nine items give energy back, from a handful of points up to the hundred that an 
Energy Potion III carries, and the cooked dishes sit in the middle at twenty five to fifty.
The catch is that several of them charge sanity for the energy. A 
Baked meat is forty energy and ten insanity, a 
Fried egg is thirty energy and fifteen insanity, which is a bad trade the moment your ceiling starts to matter.
A few pay the other way. 
Chocolate is fifty energy and takes twenty insanity off, 
Berry Pie is thirty and takes three, and both are worth saving for the moment the tank has shrunk rather than eating on sight.
The sauna buff runs for an hour, which is the longest of any buff in the game, and while it is up every food is worth about a tenth more. 
Bread goes from eighteen to twenty, 
Cheese from fifty to fifty five, and a cooked dish gains three or four. Eating a stack of food straight after a visit is the cheapest energy in the game.
Where the energy goes
Gathering charges per swing and the rate varies more than it looks. A sand pit is one energy a swing, a clay spot and a stone source are two, and a full grown tree is four, so an afternoon of chopping empties the bar four times faster than an afternoon of digging.
Benches charge per tick of the craft instead, which is why a long craft can cost more than the materials in it. The number is printed in the craft window next to the duration, and it is worth reading before you queue ten of something.
The one lever on all of it is mastery. Clearing a node faster means fewer swings, and fewer swings means less energy, so a bought level pays for itself in food you did not have to eat.
Two days without sleep and the game starts charging you twice
Go two days without sleeping and you pick up a lack of sleep debuff, and it changes the arithmetic rather than just nagging you. While it is on, every point of energy you spend also adds half that much insanity.
So an afternoon of chopping that costs sixty energy also puts thirty insanity on you, which takes thirty points off the ceiling you were refilling toward. The tank shrinks while you work.
The second half of the debuff is meaner. Anything that would remove insanity is halved while you have it, so the cures you would reach for are working at half strength exactly when you need them most.
Nothing else removes the debuff. Sleeping takes it off and subtracts twenty insanity on top, but only once your energy has filled, so a nap does nothing: you have to stay in bed until the bar is full.
The game also refuses to let you sleep on a full bar unless you are carrying the debuff, which is why the option sometimes does nothing when you are tidy and rested.
What a day looks like when you run it properly
Sleep until full, visit the sauna, eat through your food while the buff is up, then work until the bar is low and sleep again. That is the shape of a day, and time runs fifty times faster while you are asleep, so the sleep itself costs almost nothing.
The mistake to avoid is working through the debuff because the jobs are nearly done. Every hour past the two day mark costs you energy at face value and insanity at half again, and the insanity is the part that lingers after you finally sleep.
Graveyard Keeper 2 energy FAQ
How do you restore energy in Graveyard Keeper 2?
Eat or sleep. Seventy nine items give energy back, and sleeping refills the bar completely. Food is the faster of the two and sleep is the only one that also clears a lack of sleep debuff.
What is the maximum energy?
A hundred minus your current insanity, so the bar shrinks as insanity rises. You start the game at ten insanity, which means a ninety point ceiling, and at the eighty insanity cap you are working from twenty.
Why is my energy bar getting smaller?
Insanity is rising. It is the only thing that moves the ceiling, and the commonest causes are food that charges sanity for its energy and working through a lack of sleep debuff.
What does lack of sleep do?
Two things, and the second is the one that hurts. Every point of energy you spend adds half that much insanity, and anything that would remove insanity is halved while the debuff is on. Sleeping is the only cure.
Why will the game not let me sleep?
Because your energy is already full and you have no lack of sleep debuff, in which case it decides the sleep is not needed. Spend some energy or wait for the debuff and the option works again.
What is the best food in Graveyard Keeper 2?
Chocolate, for the moments that matter: fifty energy and twenty insanity removed in one item. For bulk, anything cooked eaten straight after a sauna visit, because the sauna buff adds about a tenth to every food for an hour.
