I’m sure this is very upsetting. Although what you are reporting is not on the list of usual side effects for Lamictal, it’s still possible that what you are experiencing is a reaction to the drug. In all cases, when someone has unusual thoughts or feelings (physical or emotional) when taking a drug, she should immediately contact her doctor to talk about it. Because a reaction is rare doesn’t mean it’s impossible.
One thing troubled me in your letter, though. You said the same thing has happened to you in the past. You didn’t mention if it happened while you were taking the same drug. If not, it calls the possibility of a side effect into question. Then it could be that your negative thoughts are a symptom of your bipolar disorder.
In either case, do make an appointment with your prescriber right away. It’s always wise to work with your doctor when on psychotropic medications. To do a good job, your doctor needs you to be an accurate and timely reporter.
I wish you well.