Laying down or sitting down side of head twitch or pulse. not always but throughout the day. no pain associated with it. why?

Muscle fatigue: Muscles will often twitch when they have been fatigued and then are resting. You may also feel your pulse when you are relaxed and that could be what you're feeling. Sometimes if there is a nerve that's irritated it can cause twitching and cramping but that's usually lower extremity and associated with some pain. Not to worry nothing unusual. Good health