What is it?
Hypochondria, also known as illness anxiety disorder, means being unreasonably anxious about being ill to the point where the anxiety negatively affects everyday life. Hypochondriacs often interpret harmless physical or psychological happenings, such as the noises sometimes produced by our intestines or heart palpitations, as a sign of a serious condition. The worries of hypochondriacs usually persist even after they have been examined by a doctor and reassured that there is nothing wrong with them.
The prevalence of hypochondria is hard to measure. In primary care settings, however, it has been estimated to affect around 0.8-4.5% of people.
What causes it?
Hypochondria seems to be fairly unrelated to heredity. It is often accompanied by other psychological disorders, like bipolar disorder, depression, and OCD. It can be triggered by stressful life events. Someone close to a hypochondriac may have died or developed a disease, or a parent with excessive worry about their child’s health may have “transmitted” that worry to the child. Certain personality traits, like high neuroticism, probably make a person more vulnerable to these kinds of triggers.
What happens during it?
I was surprised about how little content I was able to find about the mechanisms of hypochondria, given how distressing to its sufferers and common it is. The following is just my own speculation, and as I’m not a scientist or a health care professional, please bear in mind that I might be completely wrong.
Our brains produce hierarchies of probability to help us navigate in the world. If you think of, say, the room you’re sitting in right now, you probably think it’s quite likely that it exists now and continues to exist in the future. You might also acknowledge that there is a very small possibility that it is just the imaginary construct of your mind and doesn’t really exist, or that after five minutes a meteor will fall through the roof and destroy it. You act like the room exists now and in the future, because your brain realizes that given what you know about the circumstances, that is the most useful strategy. It might be that hypochondria occurs because the brain’s ability to produce these hierarchies goes wrong. It gives too much value to things that should be lower in the hierarchy. For someone whose brain acts like this, having multiple sclerosis might seem like the most plausible explanation for muscle weakness.
Our brains also regulate the way in which we react to things based on our current responses. Say you’re afraid of spiders.When you for the first time saw a spider and decided that you don’t want to get too close to it, your brain classified it as “something to avoid”. The next time you saw one, you might have left the room. Then you might have killed the spider. Then you might have called someone else the kill it. Then you might have ran out of the house trembling with fear. Spiders aren’t that bad, when you think of it, but just by taking cues from your own reactions, your brain has come to the conclusion that they are perfectly comparable with ax murderers. In the same way the negative feelings associated with hypochondria may be the result of this loop of going from one reaction to another until something as normal as occasional heart palpitations cause horror.
How can it be treated?
Cognitive behavioral therapy has been found useful for the treatment of hypochondria. In it the patient is encouraged to challenge their counterproductive ways of thinking. There is some evidence that the neurotransmitter-affecting SSRIs might also be effective.
Sources: https://en.wikipedia.org/wiki/Hypochondriasis, http://emedicine.medscape.com/article/290955-overview, http://www.nhs.uk/conditions/hypochondria/Pages/Introduction.aspx