I always send home a packet of information including this subject, but would gladly explain to you the importance of preventing your Chihuahua going into a hypo-glycemic shock.
This is a problem commonly known in small breeds, but seen more often in Chihuahuas. It basically means that your puppy has low blood sugar and can happen easily if they do not eat. This can be brought on by stress or even after a hard play time. Being weaned, going to a new owner, changing food, being scared or lonely in their new surroundings can trigger this condition.
Prevention is best, but if caught early enough, it can be reversed.
If this condition is left untreated, it becomes life threatening.

All new owners need to be aware of the sign and take immediate action. Early signs are pale gums, listlessness, lethargy, refusal to eat, and staggering.
If not treated immediately, it can progress to a more critical stage that includes the following, vomiting, diarrhea, seizures, unresponsiveness and even death.

For my smaller pups, I will always have hard food and fresh water readily available at all times. Only during crate training do I start to schedule feed.
Usually a puppy will show signs of this condition soon after weaning and should have outgrown it prior to leaving the breeder.
However, for some tiny puppies, especially those projected to be "teacups", the condition can present it self the first time as late as 16 weeks old.
And could possibly continue throughout their lifetime.
It comes on fairly quickly, but can be reversed just as quickly.

I recommend that anyone obtaining a chihuahua puppy from me or anyone else, continue to feed the puppy the same food that it has been accustomed to eating. Changing the food can cause stress, which can lead to refusal to eat, that can lead to hypo-glycemia.
I also recommend that you also buy a tube of Nutri-cal and always have this handy, especially if you are a owner of Chihuahuas.
At the first sign that your puppy is not acting normal or hasn't eaten much, squeeze a bead, the size of a marble onto your finger and let the puppy lick it off or gently rub it off inside the roof of the puppy's mouth or inner cheek. Continue this ritual every 2 hours until your puppy starts to act normal again. Having Nutri-cal readily available should snap your puppy right out of it in minutes
I have also included in your packet information to making a emergency solution out of White Karo Syrup thinned (50/50 with water) or you can also give them a little bit of honey.

I will also administer Nutri-cal to your puppy 24 hours before going to their new home. This is to prevent hypo-glycemia occurring en route to you.
This is also known as "carb loading". If you have Nutri-cal on hand when puppy arrives, please give the puppy a dose and then every 2 hours until you see them eating normally. You will need to keep a close eye on your new puppy for at least a couple of weeks until they are settled in and comfortable with their new surroundings.
Give them a small dose of Nutri-cal if you must leave them alone for a long time during the first few days before you leave and when you return. Remember that even tough you want to play with your new baby, they are just that- a baby!
They need plenty of rest and eat very often. Playing too hard for too long can also bring on this condition.
Again, in most cases, hypo-glycemia doesn't occur, but you need to be prepared to recognize the symptoms and know what to do when you see them. Prevention is key and having Nutri-cal on hand to give any time you think your little baby isn't getting enough to eat can prevent the condition from happening. Those who want to travel with their chihuahua will find this very handy to take along with them until the puppy becomes used to going to new places with you. It doesn't need to be refrigerated and has a long shelf-life.
IF AT ANY TIME YOU NEED MORE INFO. ON THIS CONDITION, PLEASE DO NOT HESITATE TO ASK. YOU CAN CALL ME AT ANY TIME.

thank you for this information, I had no idea

by the way where does one get this nutri-cal?

You can find Nutri-Cal in most any pet store.  I picked up a tube at Petco.

thanks you again, I will pick some up today.

When I leave my house my bambi wont eat....and i leave food...he wont eat till i get home why is that? when i first got him he ate on his own...now i have to be home...

hes 9 months....ive had him 3....any thoughts?

You have probably inadvertantly trained him to eat when you are present.  Have you tries leaving some food out in a familiar spot for him? If he sees/smells  it he might be tempted to nibble.

I keep a bottle of honey on hand for just this reason. Also, when we travel I make a point to stop and feed her regularly as well as keeping her favorite treats on hand in the car with us. I wish more breeders would mention this to new Chi owners since it is such a serious and common condition for chihuahuas.