When a Migrainuer does experience the headache phase of a Migraine attack, it generally lasts from 4 to 72 hours (untreated or unsuccessfully treated). The International Headache Society's International Classification of Headache Disorders, 2nd Edition, defines status Migrainous as:

Description: A debilitating Migraine attack lasting for more than 72 hours.

Diagnostic Criteria:

A. Typical of previous attacks except for duration.

B. Headache has both of the following features:

1. unremitting for more than 72 hours
2. severe intensity

C. Not attributed to another disorder

A general rule of thumb recommended by many Migraine specialists is:

If moderate to severe Migraine pain lasts more than 72 hours, with less than a solid four-hour pain-free period, while awake, it should be considered an emergency requiring an office call or a trip to the emergency room.

Why is it important that status Migrainous be treated?
The pain of a Migraine is from dilated blood vessels in the brain and the inflammation of tissue and nerves around those blood vessels. Extended dilation of the blood vessels puts us at increased risk of stroke. Thus, it's important to stop a Migraine attack, as opposed to simply masking the pain with pain medications, as soon as possible.