Short answer
You are tired when a blue bubble with "Zz" appears at the top centre of the screen. It comes from staying awake for roughly two in-game days, not from an empty energy bar. While it is up, every action costs extra energy and insanity rises faster, and the only cure is to go to bed — food, beer and pies do not remove it.
Home and garden
View full-size image ↗Official promotional screenshot · © Lazy Bear Games / tinyBuild · Official media kit · Material credits
How to tell you are tired
Look at the top centre of the HUD: a blue bubble with "Zz" marks appears, with a sound cue, when the Lack of sleep status kicks in.
It arrives after about two in-game days without sleeping, regardless of how much energy you have left.
That is why many players are confused by it — you can have a full bar and still be tired, or an empty bar and not be.
Tired is not the same as low energy
Energy measures how much work you can do right now. Running it to zero stops you acting until you eat or rest, but it does not make you tired.
Tiredness measures time awake. Eating keeps the energy bar going, but it does nothing for the clock that triggers the Zz bubble.
Treat them as two separate meters: food handles energy, the bed handles tiredness.
What being tired costs you
Until you go to bed, every job burns more energy than it normally would.
Insanity also builds up faster from the work you do, and rising insanity shrinks the energy you can actually use.
The result is a spiral: the longer you push through, the less each meal gets you. Sleeping as soon as the bubble appears is almost always cheaper.
Morgue and graveyard work is what raises insanity. Official screenshot; it does not show the Zz status icon itself.
View full-size image ↗Official promotional screenshot · © Lazy Bear Games / tinyBuild · Official media kit · Material credits
How to get rid of it
Walk to your bed and use the Sleep prompt. It is the only way to remove the status.
When you wake, the blue Zz bubble is gone and your energy is topped up.
Sleeping also removes a fixed chunk of insanity rather than a percentage, so a heavy build-up can take more than one night to clear.
Sleeping when you are not tired does little for insanity, so the bubble is also your cue for when a night in bed is worth it.
The purple part of the energy bar
If part of your energy bar turns purple, that section caps how much energy you can hold, and food only refills up to where the purple begins.
It builds up from morgue work such as autopsies and digging graves; beer and body fat add to it as well.
Guides report it takes roughly two or three nights of normal sleep to clear fully, so keep a regular day-night rhythm rather than expecting one sleep to fix it.
During the day, Berry Pie from the Kitchen Oven is the stop-gap: each one removes 3 insanity and restores energy.
