About a month ago, I took myself off a medication without first contacting the doctor who prescribed it, a step I have often cautioned others never to do. A neurologist had put me on the anticonvulsant drug Keppra as a preventive in case a seizure had caused an otherwise unexplained fall on my head and brief memory loss.

The neurologist was being appropriately cautious. Two years earlier, I’d had an equally mysterious accident accompanied by about a 15-minute memory gap.

A heart rhythm disorder was ruled out, and it would be weeks before I could undergo a three-day brain wave study to check for seizure activity. But after 10 days on Keppra, which the label warned could cause drowsiness, I was far worse than very sleepy. I could barely function. I was spending the day in bed, unable to work, read or even watch TV. And I was depressed, enough so that I began to list activities I could cancel, maybe even life itself.

When a friend told me she had been very fatigued and depressed while taking a different anticonvulsant, I had to know whether my symptoms were caused by the head injury or the drug, and the fastest way to find out on a Saturday night was to stop taking the drug. Within 36 hours, I was a new person, nearly back to my normal level of energy, ability to work and enthusiasm for life.