5yo son with slow brain waves

Hi, everyone. I'm a new mom to epilepsy. My son just turned 5 at the end of December and had his first seizure (to our knowledge) at the end of January. It was tonic clonic, we went to the ER, and everything was normal and looked good. The next day we saw the neurologist. 8 days later he had his second, we started Keppra. He has continued having seizures, but they are apparently tonic clonic seizures that don't spread or reach the typical climax. The first 3 seizures he had were tonic clonic, always at 6:15am, he let out a loud yelp and the seizure lasted roughly 1.5-2 minutes. Now the seizures are more atonic like.....they are irregular, his head drops, his body is limp, he sort of grinds/chomps his teeth, but he is non-responsive. He frequently complains of being sleepy and his tummy hurting after the seizures. He had a normal MRI and had his EEG last week and the doctor had us come in the next day. She said she is very concerned because his brain waves are very slow. There was a lot of info given in the hour she was with us, but it was hard to process when no one predicted anything abnormal would show up. She said he does have primary generalized epilepsy (now added Onfi to the Keppra), but she's very concerned about his slow brain waves and wants us to redo the EEG in early April after he has been on new meds for a few weeks. She also believes (from the EEG) that he is most likely having Absence seizures often and regularly, but we haven't seen them except during the EEG during the hyperventilation test. She said we also need to do genetic testing to rule some big things out. After researching, I realize she's concerned about LGS. My son is very smart, advanced cognitive skills, no behavioral issues or any developmental delays. The doctor said that after spending more time with him, she completely agrees that he doesn't fit any of the "typicals" for the big concerning issues and that she guesses he probably had a seizure early that morning and we just didn't know, so the EEG was abnormal. Would a seizure cause an EEG to have such slow brain waves? I've read that kids with LGS can be completely "normal" (for lack of a better term) before the diagnosis, I just don't see how he could possibly be a candidate for LGS. Does anyone have any experience similar to this?? I also wonder how quickly do the LGS developmental delays and overall decline start happening? Should we already be seeing those? I just don't know that I can wait 6 weeks to see if the EEG is still abnormal and then wait who knows how long after we would have to wait for genetic testing. Any help or advice is greatly appreciated. I feel so lost, helpless, and terrified. I have no one around me that has been through anything like this, but I need to be able to talk through it. My husband is wonderful and we talk often about everything, but we are both blind going through this. Thanks so much!