Clarifaction:
Just to be clear im definitely not a doctor.

Summary:
Stamina is similar to the Hunger we have, if we dont manage our Stamina correctly and over push our limits we get slowed and suffer debuffs until we regain Stamina again(max Stamina is 80).

How to lose Stamina:
Running/sprinting, jumping, swiming, attacking, getting attacked and placing blocks.

How to regain Stamina:
Walking/standing still, crouch(sneaking), eating food(+10 Stamina) and resting/sleeping(making it work very well with Comforts mod).

Effects:
Energize: make the Stamina regain factor better(regain more Stamina).
Enduring: actions drain 50% less Stamina.

Potions:
Enduring Elixir: Crafting: Mundane Potion and Golden Apple.
Energizing Elixir: Crafting: Mundane Potion and Chorus Fruit.

Tags:
There are tags that can be used in datapacks/kubejs to let other items to be affected by the mod Stamina system.
Weight tags, if the player wear armor piece with that tag the Stamina system will act accordingly:

Feather Weight (feather_weight) - increase the stamina regain factor(only the turtle helmet have this tag).
No Weight (no_weight) - not in use atm, any armor that dont have Weight tag wont affect the stamina.
Light Weight (light_weight) - Stamina actions drain 0.05 more(Leather and Chainmail).
Medium Weight (medium_weight) - Stamina actions drain 0.1 more(Iron and Gold).
Heavy Weight (heavy_weight) - Stamina actions drain 0.15 more(Diamond and Netherite).

Food & Drink tags:

Energy Food (energy_food) - Gain +30 Stamina(Only check for Food items, the mod give this tag to the Golden Apple).
Energy Drink (energy_drink) - Gain +30 Stamina(Only check for non Food items(don't give this tag to non consumable items), the mod give this tag to the Honey Bottle).
Energize Food (energize_food) - Gain the Energize effect(the mod give this tag to the Golden Carrot).
Energize Drink (energize_drink) - Gain the Energize effect(the mod give this tag to no item).
Enduring Food (enduring_food) - Gain the Enduring effect(the mod give this tag to the Enchanted Golden Apple).
Enduring Drink (enduring_drink) - Gain the Enduring effect(the mod give this tag to no item).

Tip: don't forget to take off your heavy armor when you at your home or a safe place.

And Lastly the Stamina regain factor increase by our Levels, the higher level we are the more Stamina we regain.

Using Sparkierkan7 Realistic Stamina Mod as base(https://modrinth.com/mod/realistic-stamina), big credit.

Don't forget to take a moment to rest and breathe!

Heartbeat