This is the actual migraine or “headache” phase of a migraine, following the aura phase, if present, or the prodrome phase for those without an aura. Pretty much anything I can call this phase is deceptive. Describing this period as the “actual migraine” implies that the other phases are not part of the migraine. (Not true!) And it’s equally ridiculous to call it the “headache” phase, since a sufferer can have an entire migraine without an inkling of a headache. However, these are the titles commonly given by academia, and most familiar to migraine sufferers, so we’re just going to stick with it, for now. Some may also refer to this phase as the "prostration" phase.
As the name suggests, this is the stage of the migraine in which the headache usually occurs. The severity of headaches varies from person to person and from migraine to migraine. A headache may start off mild and remain mild, or may gradually increase in severity over hours, or even days. Some migraines increase in severity so rapidly that the sufferer may not have an opportunity to take any medication. A migraine headache is typically unilateral, with pain only in one hemisphere in the brain. The headache often consists of throbbing or pounding pain, usually worsening with physical activity. The pain may shift from one side of the head to the other, sometimes occupying both hemispheres. Additionally, pain may be present in the face and down the neck and back.
Other Common Symptoms
Headache pain is not the only major symptom of a migraine. Many sufferers experience nausea, some to the point of actual vomiting. Some migraines wholly consist of nausea, with no headache at all. Migraine may include a feeling of pressure in the head, and around the sinuses, along with a runny nose, which may lead to an incorrect diagnosis of a sinus headache. Additionally, the aversion to light, sound, and smell (photophobia, phonophobia, and osmophobia) discussed in the prodrome section are all also common symptoms occurring during the main “headache” phase of the migraine. 
- Oliver Sacks. Migraine. First Vintage Books, 1999, p.110
- Tepper, Stewart J., M.D. Understanding Migraine and Other Headaches. UP of Mississippi, 2004, pp. 9-10