Stamina

Stamina is a hidden attribute that is affected by Will, Constitution, and the Distance Runner feats. Stamina effectively limits the amount of times you can use skills, special actions and stairs, or perform prostitution. 

When your character has less than 50 stamina, you will have the Tired status effect (and later Very Tired, and VERY Tired), which reduces speed by 10% and causes a chance for further attempts at using the ability to fail while still spending stamina ("You're too exhausted!"). Tired status seems to take place at a surprisingly high value - less than 50 stamina remaining. Very Tired occurs at less than 25 stamina, which reduces speed by 30%, and VERY Tired at negative stamina and reduces speed by 60%. 

If you are tired and attempt to use stairs, you may "lose your step and roll down", taking damage. This happens even if you are going up (i.e. you will end up at the floor above instead of being forced to remain on the floor you were trying to ascend from).

Stamina starts at a base value of 100. Willpower and Constitution increase max stamina by 1 for every 5 pts. The calculation for Stamina is as follows: Max Stamina = 100 + (will + con) / 5 + featstamina * 8

Testing reveals that two points of stamina appear to be recovered roughly every 7 or 8 turns, regardless of what it is you are doing (standing still, walking, melee, casting, firing bows, etc. all recover at the same rate), but actively Resting puts you into auto-turn mode for 50 turns, and appears to recover something in the area of 25 stamina.

The 1.56 Elona+ update had adjusted stamina regeneration to 2 points for every 4 turns.

Stamina can be recovered by drinking the potions blue capsule drag [sic] or soda; soda can be bought at the Festival of Jure.

Skills that use stamina:

• All special actions and activated skills have their own stamina requirements.  
• Cooking (10 stamina per meal cooked)
• Fishing (?? stamina per turn)
• Mining (?? stamina per turn)
• Performing (20 stamina per performance)
• Climbing stairs also consumes 15 stamina.
• Taking/putting an item or stack of items to/from the 4-dimensional pocket takes 10 stamina.
• Picking up a handful of snow in Noyel takes 10 stamina.

In Elona+, current and maximum stamina is shown in a display in the lower right part of the screen.

Additionally:

• Worshipers of Kumiromi recover one stamina point every other turn.
• Using the blood drain special action will absorb stamina from the target and add it to the user.
• The regeneration hex increases the rate that stamina recovers.
• As of version 1.55: When the player eats "Uh-uh, the taste is so so", or "The taste is not bad" food, or better, stamina recovers by enchant level * 1.5 + food tier.
• In addition to its other benefits, praying will recover your stamina to maximum.