"It's almost like somebody is pouring liquid Drano into your brain," says neurological patient Kirt Kessler.
"The principle nerve involved is the trigeneal nerve to head and to eye," says neurologist Dr. William Young.
You might be wondering what exactly these two are talking about. They're talking about the agony of cluster headaches, dubbed a 'suicide' or 'killer' headache.
It's estimated about 500,000 people, or one in 1,000, suffer with cluster headaches. They can be episodic, occurring in the same season or time of day, and chronic.
Dr. Young says there has been very little research funding to find a cause or a cure, but we know one thing that is proving to be effective is oxygen. Some patients like Kessler carry it with him.
He says the oxygen can reduce an attack that would normally last up to three hours, to about 15 minutes.
If you suffer from cluster headaches, you might ask your doctor about oxygen treatment to see if that might be an option for you.