Maybe if your condition causes chronic pain any sort of 'exercise' could cause the twitch as your muscles will repair after any sort of exertion at all? Have you done anything that could affect that area, even just sitting or sleeping differently?
I've had it where my muscles in my arms twitch and are clearly visible. I didn't do anything as what the GP said made sense. I get it now and again. Can you make a telephone/face to face appointment with your GP about it?