Trances are a group of active auras in the Dream Mastery. There are three of them, but only one can be active at a time.
Trance of Empathy: Force enemies to share the damage they inflict upon you by forming a telepathic link to their minds that conveys only pain and siphons life in retribution.
Trance of Empathy reflects a portion of the damage you receive back at the enemy and causes a portion of the damage you deal to heal you. This trance is best suited for characters that focus primarily on defense.
Trance of Convalescence: A restful state of mind causes increased life recovery and damage absorption for the player and their allies.
Trance of Convalescence causes your health and energy to regenerate at a faster rate and also reduces the amount of damage you receive from all sources. This trance is the foundation of any build that focuses on health regeneration. The best classes for that are the Templar (with Rally and Adrenaline) and the Haruspex (with Herbal Remedy). However, damage absorption is a very useful bonus, and so this trance is a good default choice for any character.
Trance of Wrath: Waves of negative psionic energy emanate from the player, disrupting enemy thoughts and burning through their physical being.
Trance of Wrath empowers your weapon attacks and causes them to inflict Electrical Burn damage over time, reduce enemy resistances and disrupt their skills. This trance is a good choice for casters due to the resistance reduction effect. The class that will benefit the most from this trance is the Prophet, as +% Lightning Damage bonuses will increase the Electrical Burn damage caused by Trance of Wrath. In any case, it might be a good idea to put one skill point here, as the skill disruption effect is useful against several dangerous abilities, like Onslaught used by Formicid Captains or Melinoe Blade Dancers.