If you play the violin a lot and your posture when doing so is incorrect, you might experience health issues. Pain might affect your neck, hands, arm, and back; therefore, getting into the right position from the very start and trying to maintain it every time you play will contribute a lot to keeping such pains at bay.
Ask your teacher to help you adopt the correct posture and try to keep it so as much as possible. You should keep your head straight and not tilted to one side. It is very difficult not to bend your head and neck, though, so when that happens make sure you take a break and stretch your neck muscles.
Besides posture, you need to pay attention to the technique you employ when playing the violin, the instrument set-up, the number of hours you spend playing, and what you can do to relax your muscles after your practice sessions. If the muscles and joints are not in a neutral or optimal position, you can experience strain injuries.
Intense or long practice sessions without rest will affect your muscles even if your posture is correct; therefore, taking regular breaks is mandatory if you don’t want to experience pain after your rehearsal is over.