As I said, I have no knowledge in hardware at all..
I just thought I would have to use an accelerometer to get the movements, and I would have to attach it to something to process the information, and then arduino came to my mind. I'm not really sure why I choose arduino, I just read something about it here and there, and it just seems fit.
I'm not sure if a webcam would be of use, if the movement is too small it would not be caught, and I would also have to concern about enviroment light, etc.
My idea is to have arduino plus the accelerometer sitting in bed as the subject sleeps, and then connect it to a pc to collect the data. Is there something wrong? Is this not how arduino is supposed to work?