Dreaming

The dreaming is a medical condition that occurs when long lived or immortal creatures reliant on mana find themselves without it.
    Once they have run out of personal mana resources, and if they are unable to replenish it in some manner, they will slip into a death like state until they regain enough mana from their environment to waken.
    If they are in the death like state long enough or if they only regain minimal levels of mana they may forget who they were, and exhibit signs of dementia.
     Persistent and prolonged lack of mana will cause them to live what to them may seem like a series of separate lives in which they move through wakefulness to dementia to the death sleep and back to wakefulness. Remembering only their previous lives as dreams and later as part of their dementia as they decline towards their death sleep.
     In some cases they can not gain enough mana to re-awaken and will continue in their death sleep for thousands of years.
     The dreaming happened to all magical races in Gaia once the magic was drained from the world.