1.- No, I haven´t Know anyone ever suffered from RSI or SAD
2.- Yes, when I use a computer for a long periods of time I have pains in my back because I don´t sit correctly.
3.- When you use a computer for a long periods of time you Should take a rest like, stand up and walk, put your hands over your head, try to sit correctly, bend you head to the left towards you shoulder.
4.- Yes, I think that exercises are very useful and effective because help to relax and rest your body.
5.- Yes, I do some exercise while working for a long period of time. I stand up and walk, down stairs and rise my arms.