thanks for writing to healthcaremagic.com
In all probability the level of fluctuation in BP mentioned by you is not responsible for your giddiness. Continue to take medicines prescribed by your doctor for hypertension
For your Complex migraine
you should see your neurologist
and discuss this problem of giddiness with him only. if he suggests or do not find any neurological cause for same , please see your ENT (ear specialist) doctor.
All drugs have potential to cause some side effects in certain individuals but dont worry, if one medication for migraine prevention did not suits you, some other drug may. so consult your neurologist and get relief from sufferings.