You drank too much coffee (energy-drink, Mate-tea, whatever), because you were tired, and thus did not fall asleep early enough You spent too much time on a screen at evenings / night You drank alcohol (no matter how much) the day / night before You spend you’re work day in front of a computer and barely stand up and stretch All your muscles (especially neck muscles) are tensed, because you only sit, drive, sit, lay down and never walk, run, stretch