:headbang:Yes, I have experienced something similar. Turned out to be a thyroid nodule that had to be removed surgically (just last week, as a matter of fact...still wondering when I can play again). Take a very good look in the mirror...are the two sides of your neck symmetrical, or are they uneven? Do you notice any swelling or a lump? Regardless, have it checked out by a doctor. Could be a virus as you suggest, but it could be something more. I see you're in Australia now, but here in the states, the type of doc to see would be an ENT, also known as Ear, Nose, and Throat, also known as otolaryngologist.
I second the Froggy's recommendation. Playing sax occasionally leads to discomfort due to a fairly small number of common irritants:
1) teeth digging into the inside of the lip
2) aggravation of an overly-sensitive or aching tooth
3) a little less commonly....inflamation of the Temporomandibular joint (which leads to a clicking/popping sound when you chew, speak or play the sax).
I'm no medic but it seems like playing with an open throat should not be a factor. Realistically the throat has a maximum point when it is at it's most relaxed and one cannot expand the throat beyond that point. An open throat is a fairly natural thing which should not involve strain.
Pain exists for a reason, heed the message. Yeah it could be nothing. Be smart, see a doctor.