My husband was on 100 mg of lamictal. He has since stopped taking it cold turkey.?

He has been feeling overall just sick. I guess kind of like a cold. Is this a normal reaction? We have moved on to another medicine for him. Just wondering if the headaches should be a concern. He has no history of seizure but I know this could be a side effect if he stops suddenly but we did not have the money to buy both prescription. Please help.