If you have epilepsy, understanding the potential effects of using essential oils and aromatherapy is important. Unfortunately, the research about essential oils and epilepsy to guide you is sparse.
Although it's possible some essential oils may trigger seizures, sources differ on which oils people with epilepsy should avoid.
In the book Advanced Aromatherapy, Kurt Schnaubelt, Ph.D, recommends that epileptics avoid anise, fennel, hyssop, nutmeg, parsley, and sage essential oils.
In the book Aromatherapy for Dummies, aromatherapist Kathi Keville recommends avoiding hyssop, lavandin, rosemary, sage, spike lavender (not true lavender, which might help reduce seizures), and thuja.
The paper Plant-Induced Seizures states that 11 plants are powerful convulsants, because they contain highly reactive monoterpene ketones, such as camphor, pinocamphone, thujone, cineole, pulegone, sabinylacetate, and fenchone. The plants are:
The results of the study Anticonvulsant Activity Of Citrus Aurantium Blossom Essential Oil (Neroli) suggested that neroli essential oil has constituents with anticonvulsant activity.
To possibly prevent seizures, The Essential Oils Desk Reference suggests directly inhaling frankincense or lavender essential oil four times a day (place a drop on your palms and sniff or use a diffuser for 10 to 15 minutes). Another option is to dilute the essential oil 50/50 with carrier oil and rub 2 to 3 drops behind your ears and on the back of your neck 2 to 3 times a day.
To read about the experience of an aromatherapy student who also has epilepsy, download the paper Living with Epilepsy and Aromatic Oils.
If you have epilepsy and essential oils are something you want to use, working with a qualified professional is a good idea. Also, pay attention to essential oil safety guidelines.