What causes core body tremor?

Muscle activity: Muscle contractions and relaxations, on a very small scale, can feel like vibrations and tremors. Nerves, nerve signals, neurotransmitter chemicals, adrenalin, hormones, medications, etc... May plan a role in making muscles go into tremors or vibrations.

...: Usually caffeine, extreme anxiety even if not outward anxious, hyperthyroidism, adrenal hyper function, many stimulant medications...Alcohol can cause an inner core hypothermia...Then shivering.