It turns out that I have been diagnosed with 'Horton's Cluster Headaches'. Now, I've done a bit of online investigating and I was quite shocked to see what they actually are.
Taken from Wikipedia:-
"Cluster headache, nicknamed "suicide headache," is a neurological disease that involves, as its most prominent feature, an immense degree of pain. "Cluster" refers to the tendency of these headaches to occur periodically, with active periods interrupted by spontaneous remissions. The cause of the disease is currently unknown.
Cluster headaches are extremely painful, unilateral headaches of a piercing quality. The degree of pain involved in cluster headaches is markedly greater than in other headache conditions, including migraine. The duration of the common attack is 15 minutes to three hours. Onset of an attack is rapid, and most often without the preliminary signs that are characteristic of a migraine.
Cluster headaches are occasionally referred to as "alarm clock headaches", because of the regularity of its timing. It has been known to strike at the same time each night or morning, often at precisely the same time during the day.
In episodic cluster headaches, these attacks occur once or more daily, often at the same times each day, for a period of several weeks, followed by a headache-free period lasting weeks, months, or years. Approximately 10–15% of cluster headache sufferers are chronic; they can experience multiple headaches every day for years.
Cluster headaches often go undiagnosed for many years, being confused with migraine or other causes of headache. Medically, cluster headaches are considered benign, but because of the extreme and often debilitating pain associated with them, a severe attack is nevertheless treated as a medical emergency by doctors who are familiar with the condition."
For years I have always thought that they were migraines due to the intense pain (and also because my Mum suffers them too), but although the pain can be far greater than a migraine, they are classed differently. At last - an answer to a condition that has been affecting me nearly all of my life.