Thanks for your question regarding your 11 year old Chihuahua Babe who has become quite lethargic and quiet today
As you can imagine, there are a number of things that could be going on here with little Babe, including anything from a toxicity (hopefully there isn't anything around your yard or home she could get in to), to early gastroenteritis, or due to pain
My main concern right now would be her gum color
She could be pale simply due to shock/pain, however she could have something else going on here such as a clotting issue or toxicity (rat bait in particular - so hopefully you don't have any of that around the home or yard)
Right now, please check her mucus membranes, refill time and respiratory rate as follows:
Mucus membranes - flip her lip and look at the color of the gums. They should maintain a nice salmon pink color. Get your girl to your local Vet if they appear white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on her gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanced white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the emergency Vet.
Respiratory Rate - if she is continuously panting today this is a sign of shock and or pain and a signal for a trip to the Vet.
If the refill time is very slow AND the gums are very pale, you are best off playing it safe here and getting her seen now if you can
Hopefully her membrane color, refill time and respiratory rate are all ok
If so - you can just monitor your girl for the evening
If she is pale and lethargic, then you are best off getting her seen today if you can
For now - make sure you keep her nice and warm and keep an eye on her
Please let me know if you have any further questions
I will be online for the next half hour or so
I will switch to Q & A mode now for this reason
Please be sure to click a smiley :-D face if this has been helpful.