I'm not sure about Lamictal this way, but with other meds I've missed doses on I can get withdrawal symptoms (feeling nauseous, headache, etc) and maybe have some bipolar symptoms flare up. I would for sure call the pharmacist, or your psychiatrist, if I were you and ask how you should taper up to the dose you're supposed to take.

Mood stabilizers in general are supposed to keep the depression and mania bits at bay, at least keep them from getting so severe you can't function/wind up in the hospital.