Shearing

The core part of a magic user's being is their ability to use magic and how they use it. To become a fully-fledged Mage, Witch, or Healer, a person has to devote their life to their study. As their connection to magic is deeply rooted in the way they see and experience the world, a loss of their ability to use magic is then catastrophic. This loss of magic is called Shearing. 
Shearing is usually caused by traumatic events the magic user experiences. This could be the loss of loved ones, loss of faith, or any event that precipitated high stress and a magic user's lack of confidence in their magical ability. Shearing is most commonly seen in soldiers returning from the battlefield. The majority of these users never regain their access to magic. At present, there is no known cure for Shearing. 
Although this is not an infectious condition, it is possible in rare cases for magic users to suddenly lose their ability to use and feel the magic around them without any antecedent. These sudden Shearings are what magic users are most fearful of. Just as unknown is the rare ability to gain that access back again.
There is one other known cause of Shearing, and that is by a Witch forcefully cutting a user's ties. This is a very difficult technique that should only be attempted by high-level Witches or Enchantresses. The strain on the Witch to perform such a drastic piece of spellwork will usually result in a near-Shearing experience for the Witch. It may take several weeks if not years to recover from that type of spellwork. Despite the ramifications, there has been a rise in Shearing cases by Witches during war-times as a tactic to intimate neighbouring Kingdoms. It is suspected that a Witch's ability to Shear a user of their ties to magic is determined by both the Witch's power and the understanding and strength of the connection their victim has to magic. There have been recorded cases in which the Witch has returned the ability to access magic to the user they had taken it from. The spells used for these cases do not transfer to cases of Shearing that are not caused by a Witch.