A migraine is not simply a severe headache. In fact, there may not be a headache at all.
Many migraine headaches are preceded by visual symptoms, including bright dots, patterns or lines that can obscure vision in one or both eyes for about twenty minutes. This can even occur without a headache coming on afterwards. If a headache occurs it is often pounding and frequently accompanied by nausea, sensitivity to light and noise. The headache is not necessarily severe.
Migraine may run through families. In women, hormonal changes can bring on migraine. For example, some women get migraine during their menstrual period, during a pregnancy, during menopause or after a change in hormonal supplement dosage. In some people certain foods or beverages, especially red wine, hard cheeses and chocolate can bring on migraine. Some people find that exercise or stress can cause migraine.
If you have transient visual symptoms such as bright lights lasting for about twenty minutes, but no headache, and suspect that this might represent migraine - a so-called migraine equivalent - you can be evaluated by a neuro-ophtholmologist to rule out other visual disorders.