The restractions are good with posture. But thats a very valid point. Think of when the neck gets stiff - is it at work. do you have a desk job.
How do you sit in your chair - are you slouched?
In all the necks I see almost all of them are hugely related to posture, correcting posture by sitting up straight with the bottom at the back of your chair, adding a lumbar roll can help also, and ensuring you take breaks from whatever you are doing to go for a walk or run through some neck range of motion exercises is a good idea.