Because of your history of seizuers, I'm surprised they would prescribe imipramine to you. It is an antidepressant, and this type of drug should never be stopped abruptly. So, I suspect you are having withdrawl symptoms, and this will subside with time. I feel you should always consult with your doctor before stopping any type of medication, they know best how you should do this to prevent problems like these. It would be a good idea to let your doctor know that you have stopped the medication to insure that you don't experience any other problems.
You can try melatonin which can be bought from a food supplement store. Melatonin is basically the ''sleep hormone'' it it produced naturally from the pineal gland in your brain and light and darkness have the most influence on it's production. More light, less melatonin, dark = more melatonin produced to induce sleep. It also have powerful antioxidant effect, boost your immune system and can prevent ischemic damages.
Here's the detailed information from wikipedia about melatonin and how it works on your circadian rhythm.
''Treatment of circadian rhythm disorders
Exogenous melatonin taken in the evening is, together with light therapy upon awakening, the standard treatment for delayed sleep phase syndrome and non-24-hour sleep-wake syndrome. It appears to have some use against other circadian rhythm sleep disorders as well, such as jet lag and the problems of people who work rotating or night shifts.
Taken 30 to 90 minutes before bedtime, melatonin supplementation acts as a mild hypnotic. It causes melatonin levels in the blood to rise earlier than the brain's own production accomplishes.
A very small dose taken several hours before bedtime in accordance with the phase response curve for melatonin in humans (PRC) doesn't cause sleepiness but, acting as a chronobiotic (affecting aspects of biological time structure), advances the phase slightly and is additive to the effect of using light therapy upon awakening. Light therapy may advance the phase about one to two-and-a-half hours and a small oral dose melatonin, timed correctly some hours before bedtime, can add about 30 minutes to the advance achieved with light therapy''