Exhaustion

Some Special Abilities and environmental Hazards, such as starvation and the long-­term Effects of freezing or scorching temperatures, can lead to a Special condition called exhaustion. Exhaustion is measured in six levels. An Effect can give a creature one or more levels of exhaustion, as specified in the effect’s description.
Level Effect
1 Disadvantage on Ability Checks
2 Speed halved
3 Disadvantage on Attack rolls and Saving Throws
4 Hit point maximum halved
5 Speed reduced to 0
6 Death

If an already exhausted creature suffers another Effect that causes exhaustion, its current level of exhaustion increases by the amount specified in the effect’s description.
A creature suffers the Effect of its current level of exhaustion as well as all lower levels. For example, a creature suffering level 2 exhaustion has its speed halved and has disadvantage on Ability Checks.
An Effect that removes exhaustion reduces its level as specified in the effect’s description, with all exhaustion Effects Ending if a creature’s exhaustion level is reduced below 1.
Finishing a Long Rest reduces a creature’s exhaustion level by 1, provided that the creature has also ingested some food and drink.

Causes

Common Causes: Non-stop adventure, horrible weather effects, Frenzy Barbarians,

Affected Groups

Why it matters to players: Being exhausted is bad. There are no two ways about it. This is bad, gets worse in a hurry, and is a slow recovery. If you are suffering from three points of Exhaustion, your player character needs to go to the hospital. The only thing besides a Long Rest that can help with this is the spell Greater Restoration.
Frenzy Barbarians can enter a Frenzied Rage and gain a point of exhaustion at the end of their Rage in exchange for an additional attack as a bonus action. This is akin to something like a super form or emergency option. It’s your trump card, but you can only play it once a day safely or TWICE in absolutely dire circumstances and function in a fight. Use wisely, but swing hard. Three greatsword attacks at level 5 are so satisfying.

Why it matters to DMs: Deploy with caution and make sure all your players know what they’re getting into. This is one of the most roleplay heavy conditions so make sure to encourage them to describe why they have disadvantage on their ability checks or in how you flavor their struggle. “Your arms are sore and you can’t hold your opponent down.” “You have a delayed reaction to the noise behind you and don’t see anything.” “Despite the pain you carry in your back and how bad your fingers hurt, you manage to succeed and the lock clicks open.”
https://halflinghobbies.com/every-condition-and-how-to-use-them-in-dd-5e/#Blinded
For a full breakdown of this layered condition check out this article:  https://halflinghobbies.com/understanding-and-using-exhaustion-in-dd-5e/  or this video: