The unpredictability of seizures is a large part of what makes epilepsy so hard to live with. A study from researchers in New York City has confirmed that the most reliable predictors of whether a person will have a seizure are how stressed they feel, how anxious they feel, and how long they slept the previous night.

Predictive factors
This study, published in the journal Neurology in November 2007, was based on daily diary entries from 71 people with partial epilepsy. All participants were asked to make a daily record of:

• any seizures they had: when they happened, how long they lasted and what they were like
• how many hours of sleep they had the previous night
• whether they had taken their prescribed medication
• their levels of stress and anxiety (on scales of 1 to 10)
• any alcohol use
• menstruation.

Dr Sheryl Haut at the Comprehensive Epilepsy Management Center, Bronx, New York, USA, and her co-authors analysed the diary entries to see if any of these factors were consistently associated with an increased risk of having a seizure.

The investigators found that higher stress and anxiety scores were definitely associated with a higher risk of having a seizure. In contrast, sleeping for longer was associated with a lower risk of having a seizure the next day: for every extra hour of sleep reported, the likelihood of having a seizure decreased.

Self prediction
In addition to the factors above, participants in the study also had to estimate every night how likely they thought they were to have a seizure on the following day (on a scale of 1 to 10). Seizures were nearly four times more likely on days when participants had expected them, compared with days when they hadn't been predicted.

This result is interesting but complicated: it's possible, for example, that expecting a seizure (for whatever reason) raises stress levels which in turn make a seizure more likely. These relationships need more study to be understood.

Another point to keep in mind is that the stress and anxiety levels in this study were all self-reported. A stress score of 9 out of 10 for one person may not mean the same level of worry as the same score for another person, so we have to remember that it is self-perceived stress that appears to be associated with having a seizure, rather than 'real' stress levels.

It's still not understood why being stressed and anxious can lead to seizures. It's believed that increased levels of stress hormones and other biological changes that happen when a person is worried change the way the brain works and decrease seizure threshold.

The same research team had previously found that a subset of
people with epilepsy are much better at predicting their
seizures than others.