Thank you for using Justanswer for your question.
Are you already awake when this happens? Do you recall what sort of things you may have been thinking before this happens?
If this seems centered near the heart, there is the possibility of a heart arrythmia.
Other reasons may include electrolyte imbalances, hypoglycemia (low sugar), alcohol withdrawal, stress, anger, liver disease, hyperthyroid, certain medications.
If you have not had a physical with laboratory samples recently, it will be important to start there and see if there are any abnormalities.
If nothing is discovered and you continue to have this problem, it might benefit you to have a sleep study done.
If you have any other symptoms, please reply and perhaps we can narrow this done further.
Take care, Susan
It would be helpful for you to take your temperature when you are shaking. Even though you feel chilled and cold, you may be having a fever. It is common to feel cold when the fever elevates. If you do not have a thermometer they are available very inexpensively at most pharmacies.
This would be important information to have, and I would note on your calendar when you are having these episodes. The pattern could indicate the problem. I do think it is still important to have a physical and evaluation of the blood components and electrolyes, if you have not had this recently.