Overcast



Exhaustion reduces the character's maximum energy by 10 points for each spell cast under exhausting circumstances; the maximum can drop below zero. Maximum energy recovers at a rate of 1 point every 3 seconds (in other words, it takes 30 seconds to fully recover from one exhaustion-causing spell).

The reduction of the maximum displays as a grayed-out fraction of the energy bar, as shown in the example.

Self-inflicted
Elementalists can exhaust themselves as they begin casting certain spells; if interrupted or canceled, these skills will still cause exhaustion:
 * Energy Storage: Ether Prodigy
 * Air Magic: Gale, Mind Shock, Ride the Lightning, Shock
 * Earth Magic: Dragon's Stomp, Earthquake, Obsidian Flame
 * Fire Magic: Meteor, Meteor Shower, Mind Burn
 * Water Magic: Maelstrom, Mind Freeze
 * No Attribute: Second Wind

Two spells only cause exhaustion at the end of casting, and then only if the caster is not enchanted:
 * Invoke Lightning and Chain Lightning (if used while not enchanted)

Anyone casting Devourer Siege (while riding a devourer) will also be exhausted.

External sources
The following skills also cause exhaustion:
 * causes a second exhaustion at the end of casting;
 * exhausts the target if it interrupts a spell;
 * causes hexed foes to exhaust themselves whenever they cast spells;
 * (Monster Skill) causes hexed foes to exhaust themselves when using any energy-based skill.

The following environment effects cause exhaustion:
 * Aspect of Exhaustion inflicts exhaustion every 30 seconds.
 * Sheer Exhaustion causes all spells to inflict exhaustion.

Removal
The only way to remove exhaustion is by waiting or changing zones; there are no skills to remove it.

Prevention

 * prevents your next spell cast from causing exhaustion.