People who can speak without effort can't imagine the extent to which your voice is a core part of your personality and how much it shapes your interaction with the rest of the world.
Spasmodic Dysphonia is a neurological disorder, one of the localized dystonias caused by a signaling problem from the part of the brain that causes movement. In contrast to general dystonia, which begins during childhood with severe impact upon the ability to walk and talk, focal dystonias tend to come on in middle age and affect just one part of the body, causing a muscle group to go into involuntary contractions when you attempt to move that particular part of your body.
In the case of torticollis (spasming of the neck muscles) or blepharospasm (spasming of the muscles around the eyes), the focal dystonia can cause twisting or twitching of those muscles. Spasmodic Dysphonia (or SD as we call it) causes the muscles that control the opening and closing of the larynx to go into spasms when you try to speak. This causes breaks in your voice and sometimes a harsh vocal quality either because the larynx is slammed shut or because it's perpetually open, letting too much air flow through and making speech very breathy.
We don't know what causes SD, but it looks like there's an inherited genetic predisposition that gets triggered by something later in life. Theories abound on what actually triggers SD. It could be something as simple as overuse, an upper respiratory infection, an accident or an emotional trauma. Research hasn't yet found the answer. And, because SD is relatively rare, there's not much money for research.
So, for those of you who are lucky enough to still have all your parts working, think about going to the website for the National Spasmodic Dysphonia Association and making a small contribution so we can find a cause and cure for this debilitating disorder: