I felt this might help some people feel a bit better...
here are some common sense health checks... one or more of the following could prompt you to want to have an exam at your vets :
increased or decreased thirst
urine that is consistently almost water colored (in combination with other symptoms, dilute colored urine can also mean the dog is well hydrated
urine that is very dark in color or concentrated.
loss of appetite for apparently no reason (i.e. no stress factors or food changes involved)
vomiting
nausea- decreased appetite, lethargy, and drooling are all common signs
discoloration of the mucus membranes (gums, eye lids, or the pink part around the eye)i.e. a yellowing color
seeming uncomfortable in combination with other mentioned symptoms - kidney failure can be very uncomfortable
any change in behavior that cannot be connected to a stressor in the pet's environment.
diarrhea, especially very watery stuff or with blood
these are all things that I might mention to a client on the phone if they called...
The most important thing is, if you are worried about your pet there is probably a damn good reason why, think about what triggered your concern. Often times we will get a call and one of our tips would be that if they are calling there is probably a good reason for it and that alone may dictate the need to be seen by a vet.
If anyone has any questions please let me know and I'll do my best to answer then.
once again please keep in mind that I am not a veterinarian and it is always better to be safe then sorry when concerning an animal that appears to be ill, and just have them seen.
*edited to fix my crazy illiterate sentences - thank you head cold!*