I have personal experience with eucalyptus oil causing an allergic reaction in cats, but I didn’t realize that essential oils could also cause seizures.  Rebecca Watson posted a video about a recent study focusing on essential oils and seizures:

This was an overview of four years of data from 350 patients who experienced their first seizure or their “breakthrough” seizure (the first seizure in a very long time for a patient who had previously experienced seizures), finding that 15.7% were connected to essential oil exposure. And so that’s not just in patients diagnosed with epilepsy, that’s for everyone. 40% of the patients in the study who experienced what the researchers call an “essential oil-related seizure” had never had a seizure before, and the majority were adults.

Yet another reason for them to be kept out of my house.  (The cats are doing well by the way.)