I realize I may sound a bit alarmist but....in an older dog (and 17 is very old), syncope (i.e. fainting) is almost invariably representative of a heart problem. Age-related heart degeneration and lessening on contractility and all of that cane some on very slowly, so the dog may not show the big signs of heart failure - sometimes fainting is the only symptom.
I'd save up for the EKG, myself. Either that, or get a second opinion - some vets are better at cardiac auscultation than others. Myself, I can't hear arrhythmias very well (yet) but some of my classmates are great - it's really a hard talent to acquire, and variable. $400 is also VERY steep for a simple EKG...maybe try another vet (or state vet school for a lower price and more experienced cardiologists) for that as well.
Edited to add: I also saw in another post that Candy is epileptic... that adds a whole other dimension to it that I can't really address, not being an neurology expert, but I am sure that contributes. How recently was she diagnosed? Unfortunately, mild cardiac problems causing sporadic decreases in brain perfusion can be confused with epilepsy often. Again, I would double check the heart.