Almost half of the 990 epilepsy-linked deaths in England each year are avoidable, says a parliamentary report.
Misdiagnosis means thousands are taking drugs they do not need
Nearly 70,000 patients do not get drugs they need, while even more are given medication unnecessarily, the All Party Parliamentary Group on Epilepsy said.
It described the figures as a "national scandal", arguing that misdiagnosis of patients was costing £134m annually.
The Department of Health said it took epilepsy "very seriously" and would study the report carefully.
Epilepsy - the most common neurological disorder - affects 382,000 people in England, or one in every 131.
The panel was chaired by Baroness Gould of Potternewton and was supported by the Joint Epilepsy Council, an umbrella body of 21 epilepsy organisations.
In addition to various studies, it heard oral evidence from patients, volunteers and specialists in the sector, and concluded that - despite the development of effective treatments - 69,000 people were living with unnecessary seizures, while 74,000 were taking drugs they did not need.
Around 400 people were dying of the condition each year because they had either not received the right diagnosis or were not getting access to the right treatment.
Around half of those with epilepsy are seizure-free, but with the right care, this figure would reportedly rise to 70% - an extra 69,000 people.
The parliamentary group said the government needed to set clear targets for epilepsy care and ensure that local health bodies were following guidance put forward by NICE, the body which assesses treatments and tells the NHS whether it is cost effective to use them.
It put forward a series of recommendations, including referring more people for surgery, increasing the number of epilepsy specialist nurses, and boosting funding for those with epilepsy.
It added that there needed to be greater awareness of Sudden Unexpected Death in Epilepsy, responsible for two-thirds of epilepsy deaths and a particular risk for those who have either not been diagnosed, or whose medication is not effectively controlling their seizures.
The Department of Health noted that funding decisions were increasingly devolved to local heath organisations.
"In cases where evidence is brought to the department that local NHS is not funding NICE guidance then we will ask Strategic Health Authorities to intervene."
Epilepsy seizures occur when too many nerve cells send messages at once, producing what could be described as an electrical storm.
Epilepsy has been linked to brain damage from birth injuries, head injuries, stroke, brain tumours and alcoholism, while some seizures are thought to have a genetic basis. However, no one exact cause has been pinned down.
The report is due to be published in full on Wednesday.