Most likely, you got drug reaction because of taking Dilantin as a result of that, you got headache, heaves and nausea. This is best that you already stopped taking Dilantin. Now you are taking Levitiracetam as anti seizure medication. This is good medication to control seizure but like all medications, this could have certain side effects. Please keep in mind that side effects of medication vary from person to person as some patients who take Dilantin does not complain about hives and blisters. This is not necessary that you will get same hives after taking Levitiracetam because change of medication from one class to other could be safe for the patient. However, we have to be always on safe side and patient safety is our top priority.Get emergency medical help if you have signs of an allergic reaction to Levitiracetam: hives; difficult breathing; swelling of your face, lips, tongue, or throat. Report any new or worsening symptoms to your doctor, such as: mood or behavior changes, depression, anxiety, panic attacks, trouble sleeping, or if you feel agitated, hostile, irritable, hyperactive (mentally or physically), or have thoughts about suicide or hurting yourself. Other drugs may interact with levetiracetam, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using. Traumatic brain injury (TBI) is a major cause of seizures in the general population. Several studies have shown an increased risk of epilepsy after traumatic brain injury, depending on risk factors, such as severity and time post trauma. In your case, the chances of developing epilepsy are high as compared to normal general population but do not worry, there are good antiseizure medications now a days. I think, this would help.