Why do i get weak during and after a migraine attack?

4 to 72 hours rule: The ihs headache classification committee defines migraine as an idiopathic recurring headache disorder with attacks lasting 4 to 72 hours. The important characteristic of migraine is that routine physical activity, or even head movement, often aggravates the headache. Migraine sufferers often withdraw to a quiet, darkened room and attempt to sleep.