There is no point just being worried about this. Go get the lump checked out. I advise you to do it before the holiday period, as if suddenly needed, vet offices could be closed then for days....and worrying about it could spoil your Christmas. It is better to find out what this is, and deal with it straight away.
I can't tell you what this lump is. It could be any number of things. The vet will probably have a pretty good idea, but to be certain, may recommend doing a needle biopsy, which is fairly quick, and doesn't need anesthetic. Blood tests may be done as well, or other diagnostics if needed.
This could be ....a lipoma, an abscess, a cyst, swelling of the gland for some reason (very often neck glands swell when there are problems with the teeth or ears, or even a small local abrasion, cut, sting or insect bite)....the larger percentage of lumps found happen to be benign, statistically. But of course there IS always the possibility this could be cancer, and if so, it would need to be dealt with quickly.
So make an appointment to see the vet.
The Content on this Site is presented in a summary fashion, and is intended to be used for educational and entertainment purposes only. It is not intended to be and should not be interpreted as medical advice or a diagnosis of any health or fitness problem, condition or disease; or a recommendation for a specific test, doctor, care provider, procedure, treatment plan, product, or course of action. MedHelp is not a medical or healthcare provider and your use of this Site does not create a doctor / patient relationship. We disclaim all responsibility for the professional qualifications and licensing of, and services provided by, any physician or other health providers posting on or otherwise referred to on this Site and/or any Third Party Site. Never disregard the medical advice of your physician or health professional, or delay in seeking such advice, because of something you read on this Site. We offer this Site AS IS and without any warranties. By using this Site you agree to the following Terms and Conditions. If you think you may have a medical emergency, call your physician or 911 immediately.