One Pain at a Time

Here’s something that has been puzzling me for years. I happen to suffer from chronic headaches. And from time to time, I’ve also had knee injury, lower back spasms, toothaches, stubbed toes, minor cuts and bruises, etc. What I’ve noticed is that I never experience two or more pains at the same time. It’s like my brain can only process one pain at a time, and puts any others into a sort of “background” mode. Has anyone else noticed this, and is there any physiological explanation?