Lamictal withdrawal

My husband took Lamictal XR for 1 and a half years and recently over 6 weeks weaned himself off of 200mg per day--he has been totally off of it for about 3 weeks. He also takes Depakote ER which increases (doubles) the amouint of Lamictal in your system, so taking 200 mg of Lamictal XR while on Depakote ER is like taking 400 mg of Lamictal XR per day-- so that should really be considered as the amount he weaned off from.  We recently learned that he probably should have weaned off the Lamictal much more slowly as the withdrawal symptoms were/are horrendous. The worst withdrawal symptom seems to be insomia. Can anyone tell me how long the insomia is likely to last??? He's getting 2-3 hours of sleep at most per night--- its is so stressful!-- he can't do anything during the day because he is so tired and the nights are endless hours of torture