The pain of the cluster attack is extreme and starts very quickly, usually without an aura or a warning. Within minutes, it becomes very severe. Although the pain is usually located about the eye or temple, it may be more intense in the neck or facial areas. Although usually unilateral, the pain changes sides in 10–15 % of patients—either during a cluster cycle or the next cycle may see pain on the opposite side. The pain itself is excruciating, described in various manners as sharp, stabbing—“like my eye is being pulled out” and occasionally, throbbing.

The length of attack varies, but 45 min is the average. Cluster patients usually experience one or two headaches per day, but this may increase to as many as seven per 24 h or decrease to as little as one or two per week. They usually occur around the same time each day, with the time period 9 p.m. to 10 a.m. being the most frequent. Approximately, half of the patients awaken from sleep with the headaches.

Cluster cycles, except in the chronic variety, usually last 3–8 weeks and then stop until the next bout of clusters. The clusters occasionally last as little as several days, or as long as 5 months at which time we begin to think that they may have converted to the chronic cluster type. Ten percent of cluster patients have chronic clusters in which there is no break of at least 6 months between attacks. One or two bouts of the clusters per year are average for most patients. They may increase in frequency with only several months in between bouts or several years may elapse between attacks. When periodic clusters begin at older ages, the chance of conversion to chronic cluster becomes greater. The natural history of clusters is not known, but the tendency is for the cluster series to stop at a certain age. Many patients “lose” their clusters in the late 30s or 40s, particularly if they have had them for many years.

During the cluster series, over half of the patients are very sensitive to alcohol and most patients will have an attack triggered by ingestion of alcohol. The other “headache foods” are less important, but avoiding monosodium glutamate (MSG), aged cheeses and meats, and chocolate is prudent during the cluster series. MSG, in particular, seems to trigger a more sever cluster in some patients. Cluster patients may have their clusters after stress is over and occasionally excessive cold, heat, or bright light have been associated with the precipitation of a cluster. However, most cluster patients have very little control over the clusters, except with medication.

The typical episodic cluster series builds over 1–2 weeks and peaks for 1–3 weeks and then decreases. In the 10 % of cluster patients with chronic clusters, periods of peaks and valleys with the headaches also occur but an extended break without any clusters is not present. Chronic clusters are not usually consistent throughout the year but tend to increase in certain seasons. In managing the clusters, we keep in mind the fact that the clusters build and then peak so that I often treat them with somewhat less medication—particularly corticosteroids—in the beginning of a cluster period. The natural history of clusters is unknown. However, it appears as if the more years a patient has them, the more likely they are to abate.