Massive Migraines Following Panic Attacks?

I've been suffering from panic attacks which will just occur 'out of the blue' for the past few years.

Lately however, I have found that the panic attacks are happening more frequently (every 2 weeks or so) and lasting a few hours at a time.

After each panic attack, Ill have a MASSIVE migraine for the rest of the day/afternoon.

What causes this?

Since they are one of your triggers, it pays to avoid them! Stress of panic attacks can induce migraine. PANIC ATTACKS: View the techniques for control of panic attacks, in section 8, in my website, at ezy build, below, which I created to contain all the information that there isn't enough space for, here. Begin, on this first occasion, only, by holding your breath for 5, or 10 seconds: this will give you the confidence to realise that YOU CAN CONTROL YOUR BREATHING, but not pass out, or die (your autonomic nervous system resumes breathing, if you become unconscious). Understand panic attacks, and what triggers them, in your life (if it is unresolved anxiety, or stress, see sections 6, or 42, respectively). The paper bag method works for most people: try it. If you are fairly suggestible, the following are reliable: http://www.hypnosisdownloads.com/
Your last alternative is psychotherapy, to address its fundamental cause: read section 1, and examine the http://1-800-therapist.com/ website, and use the locators, and phone book. I used to suffer from panic attacks, until I questioned what had changed in my life, at, or just before that time, to trigger them. For some people, this is enough. These days, I have instilled the habit of, whenever a situation occurs where panic is likely, I visualise a large, flashing red "STOP!" sign, as vividly as possible, followed by repeating to myself: "stay calm" in my mind. You could try the same method. It usually takes 30 - 40 repetitions, for most people, to establish a new habit. I also suggest that you learn, then practise the controlled breathing technique, until competent, then employ it, at the very first sign of a panic attack. Practice one of the relaxation methods on pages 2, 11, 2c, or 2i, daily, and when needed. Also, give the EFT a good tryout, to see if it helps you. There is also a version for use in public places, (if you like, you can claim to have a headache, as you massage/lightly tap your temples, but you would then be restricted to subvocalising: saying it to yourself in your mind). Section 53, and pages 2, 2.q and 2.o at http://www.ezy-build.net.nz/~shaneris also refer: "Even though I sometimes suffer from panic attacks, I deeply and completely accept myself." Note: the controlled breathing only helps with the symptoms (as do medications/herbal remedies): you need to address the underlying cause, and this requires some form of therapy. Because many people can't access/afford professional therapy, I include the EFT, and EMDR variant for them to try, free of charge. Cognitive Behavio(u)ral Therapy is generally available in most areas, but EMDR (see section 33) may well be worth trying, and is becoming more widespread. (The following is a variant of EMDR therapy, which has been used successfully for those people suffering from Post Traumatic Stress Disorder, insomnia, and anxiety: it is easily learned, quick to use, yet can be very effective. It is currently the subject of much study by neuroscientists, to discover how it works. Don't dismiss it, merely because it seems a little strange: give it a tryout!). Prior to using either of the methods in the above paragraph, or using it on its own, first sit comfortably, and take a deep breath. Then, without moving your head, move your eyes from the left, to the right, and back again, taking around a second to do so (say: a thousand and one: this takes approximately a second). Repeat this procedure (without the words, although you can count, subvocally if you like) 20 times. Then close your eyes and relax. Become aware of any tension or discomfort you feel. Then open your eyes, and take another deep breath, and repeat step one, closing your eyes, and relaxing afterwards, in the same manner. Then, repeat the procedure one last time. Some people may find that this is all they need do. With experience, you may find that you can practise this in public, with your eyes closed, which greatly widens the window of opportunity for its use, and avoids attracting unwanted attention. Migraine is addressed in section 14.

Sounds like you may have been misdiagnosed. Talk to your doctor about Meniere's Disease. It's not contagious, so don't freak. Most Menier's sufferers have origionally been misdiagnosed with either panic attacks, migraines, or other similar condition. It isn't until it progresses that it becomes easier to identify. The frequency of your 'panic attacks' is rather uncommon, so you should see a doctor, anyway.