Migranes take a variety of forms, but the standard link betrween them is the swelling of blood vessels within the skull, leading to that 'one side' effect, and the side can vary, sometimes for the individual sufferer. Further symptoms can include intolerance of light and sound, nausea, and in extreme cases, temporary paralysis and loss of speech. Treatment is improving in leaps and bounds for this distressing condition, so a chat with your GP may well get you some relief.