18 month old shakes when he is first woken up. almost like an adult shiver but he is not cold. lasts about 15 minutes. should i be concerned?

Myoclonus is invol-: untary twitching of a muscle or a group of muscles. They may be benign or they may indicate a medical disorder. An EEG is needed to rule out any of the childhood epilepsy syndromes in which myoclonus occurs. Start by taking your son, a video of an episode, & completed developmental & autism-specific screens recommended for all 18- & 24-month-old toddlers, from firstsigns.org, to his pediatrician.