I am a Certified Athletic Trainer. I love my job (most days, ha!). I have not ever 'worked' a day in my life.
The upper trapezius (traps) knot up very regularly and cause you to feel tight, hunched over and can often cause stress and tension headaches. All you need as a firm self massage/trigger point ball (Lacrosse ball is great if you’re in the USA!) and do the following exercise for a great myofascial release: