first and foremost thing, many episodes of epileptic seizures are generally coincident with a history of fall and so produce confusion in diagnosis about the real cause of the incidence. but here it seems to be a case of epilepsy
only as it was associated with post epileptic period of confusion and drowsiness
. may be this seizure had precipitated the event of fall while exercise and as you said EEG also suggests some kind of seizure activity.
1. please be careful that you don't stop giving the medicine prescribed by the doctor as it may unmask the seizure activity that is suppressed at present. the drugs are withdrawn in a phased manner generally after one and half to two years of seizure free period that too with tapering the dosage of drugs. you ve to also make sure to take your child to doctor for regular follow up for the dose to be increased or decreased according to the body weight.
2. there is not much side effect of this drug and is quiet safe and will not affect the normal development of your daughter at this stage so rest assured.
3. cause of the seizure cant be ascertained in every case. as you said the CT scan
was normal any tthere is no history of fall or trauma prior to this, so it seems to be a epilepsy what is called as idiopathic, that is, no particular cause can be ascertained. but in most of the cases they are controlled well on medications. so follow up regularly with your doctor and follw the advices given .