Hello, The most commonly occurring side effects are drowsiness and an increase in appetite which may lead to increase in body weight. Other side effects such as dizziness, dry mouth,nausea and constipation have been reported infrequently.There are two possibility either it could be due to migranil or you might be having some other problem. Wait for one or two days . if dizziness still persists consult physician or neurologist for further evaluation. Some of conditions presents with headache and dizziness are migraine ,hypoglycemia, hypotension, panic attacks etc..