Hypoglycemia and hypothermia are two serious health threats to a toy breed puppy.   Together or singly, either can result in the loss of a puppy.
Hypothermia  occurs when a puppy’s body is unable to maintain its body temperature   either due to low ambient temperature in proportion to the puppies size  or low energy stores in the body.  Also , very small puppies may still have incompletely developed thermoregulatory mechanisms.  Care must be taken that toy breed puppies have supplemental heat when sleeping, not be left on tile floors for prolonged time periods, or be allowed to become hypoglycemic.  On the other hand, we must be careful not to overheat them.  
Hypoglycemia is a life threatening condition that occurs when the puppy’s blood glucose drops below normal levels. The severity of the situation is determined by several factors, including the puppy‘s activity level, environmental temperature, and  diet and feeding schedule.  Symptoms are determined by how fast the glucose level drops and how low it gets.  They may range from mild lethargy (simply being weak and listless) with a minor drop,  to lack of coordination (acting disoriented or drunk), to seizures (twitching, jerking, head pulled back over topline), to  being comatose.   With the onset of hypoglycemia, a vicious cycle developes - the lower the blood glucose gets, the more the puppy’s body temperature drops, causing the onset of hypothermia.  Hypothermia stresses the body additionally by demanding more energy to maintain its temperature.  
With this knowledge, it is usually possible to avoid these episodes.  Feed you’re a puppy a HIGH quality, high protein diet and feed it often.  I like to feed a puppy no less often than every four hours.  (I actually keep Diamond Naturals Small Breed dry in with the puppies at all times.  I prefer dry food as it is digested more slowly  and therefore utilized over a longer time period than wet.)   Be sure that the puppy has enough time with its food to eat -  the temptation to hold and play with the puppy is great, but restraint must exercised.  The puppy must also get adequate rest- they need rest periods  just like a baby.  After a round of vigorous exercise, give the puppy a snack.  Provide  supplemental heat or at least be very careful to avoid chilling as a low body temperature places additional strain on the body.    If a puppy that has been eating well does not eat, get it to a veterinarian immediately as there is an underlying cause that must be dealt with
(most often tonsillitis in my practice).   If by some chance an episode of hypoglycemia does occur, action must be taken at one.  Wrap the puppy in a fluffy bath towel immediately.  Rub honey or real molasses over the puppy‘s gums every few minutes.  (You can use Karo if you do not have honey or molasses, but I do not like anything that contains high fructose corn syrup as this stresses the pancreas.  It is best to simply plan in advance and have all emergency supplies available.)  As soon as the puppy is “awake enough” to be able to swallow, give it pureed canned food such as Eukanuba’s Maximum Caloire or Hill’s A/D with a syringe.  These two products are ready to syringe straight out of the can.  It is a good idea to keep them on hand in case the puppy does not eat a meal  so that you may force feed it ( a couple of ccs every hour) until you can get it into your veterinarian.  
Remember- in most cases hypoglycemia CAN BE PREVENTED!  If it does occur, it is life threatening and need immediate attention!