Magician's Fugue (Magical Disease, Permanent):NOTE: If already under the effect of Magician's Fugue, go to Total Recall, below.
The Magician has, in attempting to the Cast the Spell from his Mind, accidentally lodged it into a hidden part of his Psyche. The Magician, while under the effects of this Disease, has completely forgotten his understanding of the Spell that has triggered the Fugue.
NOTE: There are many variations of the Art & Science of Magic in the Multi-verse. Some Magicians Cast from a Pool of Power within their Minds through their Known Spells (known as Sorcerors or Psionics on some Planets). Others Program specific Spells into their Mind-Form that are Forgotten once Cast -- necessitating multiple instances of a Spell be Memorized if the Magician wishes to Cast a specific Spell more than once (known as Wizards or simply Magic-users on some Planes).
In the latter form of Spell-Magic, the Magician loses the other instances of the Spell in addition to the one Cast that triggered the Fugue. While in the Former, only the Magician's understanding is impacted, not the Pool of Energy utilized for Castings.
While under the effects of the Fugue, further Castings of the Spell that triggered the Fugue is impossible -- effectively striking the Spell from the Magician's list of Known Spells. This is a Permanent Magical Disease and can only be removed by way of a Remove Disease Spell or similar.
Note: Even redundantly researching the Spell so-forgotten will not bring the understanding of it back to the Magician. The Spell is a complete mystery to the Magician now.
Total Recall (Instant):If a Magician who is currently under the effects of Magician's Fugue comes under the effects of the Fugue again -- the secret part of the Magician's Mind where Spells sometimes get lodged is blasted open by the transposition of a second Spell. This results in two effects:
The primary effect of this is that the Spell that has triggered this second instance of Fugue is NOT forgotten -- AND the Spell that was originally forgotten is remembered.
The second effect of this is that the old Spell that has been remembered is immediately Cast as the Magician's total recall of the Spell is psychologically explosive -- the exact effects (targets et cetera) should be randomly determined by the DM.