Side Effect?

I’m having an experience that’s new since I’ve been taking Lamictal/lamotrigine, possibly since my daily dose was increased to 75 mg. It happens when I’m very tired and close my eyes and drift off a bit: if there is a sudden sound, I see an explosion of small white lights. Kind of like fireworks. The sound doesn’t have to startle me, just bring my attention back to the present. The phenomenon isn’t painful, scary, associated with a change in mood, accompanied by physical symptoms/movement, or anything else that would suggest it is a serious concern. It’s just… different. I’m not sure whether I should be concerned about it, but I plan to bring it up the next time I talk to my advanced practice nurse.