The vet called with Elvis' diagnosis.
The cyst/lump in his neck is something called a "sialocele" and is the result of a ruptured salivary gland. Basically, it was filled with saliva. (I know, ewww.) A blockage of some kind--a cyst or a small stone similar to a kidney stone--in a salivary gland duct most likely caused the rupture. Since the saliva isn't able to exit the gland through the duct, the gland bursts and the saliva oozes into the surrounding tissue, forming a cyst. (I know, ewww again.)
Sialoceles can be dangerous because the saliva can easily become infected and spread quickly through the body. Even though the vet aspirated the cyst, he still put Elvis on an antibiotic to prevent this from happening.
As for now, the cyst is gone but will most likely come back. If/when it does, the vet might have to remove the gland permanently or put a "stint" in it so the saliva can drain externally (I know, ewww yet again) and give the rupture time to heal.
So anyway, this is GOOD, much better than all the terrible possibilities. Elvis and I both THANK YOU for all your kind words and prayers!