Hi rosi12 - I'm currently on Flecainide for the last yr. Prior to this episode i took it for 18/12 in 2005/6. Looking back at my migraine diaries I had a huge increase in migraines as I withdrew from the Flecainide BUT it could possibly have been that i was getting re emerging ectopic beats without knowing which tend to trigger migraine as they dispupt the blood flow to my brain. Otherwise i don't recall any other withdrawal symptoms. Not much help really -sorry.
All changing, including stopping, medications must be done under the supervision of your doctor.
As to side effects going on or off it varies - no standard answer other than "yes" there are some, and for some people the side-effects are unnoticed.
I have no experience with flecainide, but I do know it is one of the stronger arrhythmia drugs and know that even a simple beta blocker may require the patient to phase-out, not suddenly stop, taking the medication.
There are many who post here who have experience with your drug, perhaps my "bump" will get a response from one.
Finally, check on any troubling symptoms with your doctor.