Mana Burn is a magical affliction caused by exposure to high levels of magical energy. Usually it comes from a magic user drawing upon too much magical energy from whatever source that may be. Most mages have a limit to the amount of energy they can either take in at one time or handle over a length of time without some kind of rest and recovery period. Mana burn can also be acquired from simply being exposed to high levels of magical energy over a short time. There's no definitive time frame, but generally is some time within a day. And like drawing upon too much energy, the person needs time away from the source of energy to sorta cleanse themselves. While the island is basically constantly thrumming with magical energy it's normally protected and not in an exposed state where it can affect people without them being able to draw upon it. Many immigrants akin the mana exposure to being exposed to nuclear energy.
The initial symptom of mana burn when the affliction is acquired is intense pain throughout the mind and body depending on how a level of energy they're exposed to. While suffering from mana burn a person experiences pain similar to a recovering burn victim. Usually a constant state of discomfort and low level pain at the best of times. A person also can't handle any magical energy, doing so just causes an intense, crippling pain like salt in a wound or sand paper over an exposed nerve. Rare cases sometimes can leave a magic user completely unable to handle magical energy or else their ability is crippled and reduced even after making an otherwise full recovery. Some people show signs of first or second degree burns on their bodies. The real severe cases leave a person with jagged lines across their bodies similar to seeing their veins. The burns and marks tend to be in strange colors usually reflecting the energy the person was exposed to. Most of the time, even with the severe cases, these marks fade and are unlikely to remain.
The first and most important is to remove the person from the source of magical energy that caused the affliction as well as any exposed sources of magical energy. Like a burn victim, usually during the first couple days the person should be kept comfortable as any kind of pressure or touching upon the skin usually is painful. This tends to fade pretty quick with most of the pain internal. Magical healers can work on someone suffering from mana burn but they must be very skilled, especially with control and shielding of their energy. Even then, despite being healing, exposure to healing magic still can cause discomfort and even pain. Healing magic can be used to help with the outward symptoms, especially those relating to burn injuries. It can also help internally to a degree with pain dampening. The best treatment though is simply rest and keeping away from sources of exposed magical energy. Their is no set recovery time, as the level of affliction can vary. Some take only days, others weeks or even longer.