Many who write suffer in silence. Millions of writers sit and write in agony, and yet dare not speak of it... it has become their Secret Shame. But it doesn't have to be that way.
If you are a writer and in pain, there is help to be found! It's only a myth that the illness only affects those who write. Seek help! You know what illness I'm talking about, do you?
I'm talking about Hemorroids.
Seriously now: sitting down for long periods of time can often lead to constipation, hemorroids and related ailments. Writers should look after their health, and get regular exercise. Get offa that chair, get up! Get down! Take a walk.
Another problem which arises over time, is neck and shoulder strain. When you sit down to write, make sure your arms are resting comfortably, and do stretching exercises now and then. You can learn more here.