Tinies are especially prone to hypoglycemia or low blood sugar, as it is commonly known. You don't have to have all the symptoms to have it, but shaking is a common symptom. Tinies just don't have the fat reserves bigger dogs have, and all dogs under 4 pounds should be watched for symptoms. If the blood sugar drops too low, another symptom can be "loss of appetite" and that's why many people use Nutri-cal or white Karo syrup, as it get into the blood stream fast and raises the blood sugar so that appetite should return within 20 minutes. You should always offer protein at this time because insulin levels are raised by the sugar, and can cause another attack of low blood sugar if their isn't some protein in the system which releases sugar more gradually. Think of protein as time released sugar instead of a hypodermic needle of sugar like Nutric-cal, or Karo syrup. Many breeders recommend free feeding for puppies and especially tinies, and they never have a case of low blood sugar. See this link for more information on hypoglycemia. It can be potentially very dangerous if food isn't given.
Hypoglycemia Symptoms and Treatment