Hi. I have the same type of migraines. Here is what I came across:
If you smile and one side of your face droops
If the pain is worse than you have ever experienced
If you lose control of you bowels or bladder,
If your migraine medications don't work,
If you can't speak,
If you can't see
Or any new strange symptom
Have someone take you to the hospital or call 911.
Whisperwolf is right, it is so important to go to the hospital or call 911 if you experience symptoms of a stroke, even if you believe they may be associated with a migraine.
If you have already been assessed by a doctor before and have been diagnosed with Hemiplegic migraine or Basilar artery migraine AND these sorts of symptoms are normal for you (and your doctor is aware of these symptoms), then you do not have to go to the ER every time you display these symptoms unless your doctor has instructed you to go to the ER (and sometimes a doctor might instruct you to always go to the ER depending on your situation). But, even if you do have diagnosed migraine with stroke-like symptoms, if you ever show any NEW stroke symptoms then it is still important to seek immediate medical attention regardless of previous diagnosis, just like the last note on whisperwolf's list says.