odd behavior - side effect of meds?

My daughter (6 years old) has absence epilepsy. She tried lamictal alone for 6+ months and it didn't work for her. Then she tried lamictal + depakote and finally got her seizures under control in July. Excellent news, except the past month or so I have been noticing some really odd behavior in her that I haven't seen before. She will get completely silly - not just the normal kid silly, but kind of crazy. She will just pick up on something to laugh about - it is usually some word or phrase, and she just laughs about it non-stop. It's not even anything that would be funny to another kid, I think. Has anyone seen or heard of anything like this? It really has me sort of worried. She probably does this once per day, and it is typically at night when she is tired. Thanks!