minxish -- You are the perfect example of being alone in a crowd, aren't you? You have your immediate family plus your parents and your in-laws to deal with. Meanwhile, inside you are worried sick that you have a serious illness. It is too bad that no one takes your concerns seriously. I'd recommend trying to see a specialist in neurology or movement disorders. But I don't know where you are located, so the process may be different from what I am accustomed to in the U.S.
You mention feeling ill, depressed, and tired. You are "pretty certain" that you have PD. Do you have other symptoms as well? I wouldn't necessarily think of PD from just the symptoms you listed; there could be many other possibilities. But if you have a resting tremor or lack of normal arm swing when walking or other symptoms more specifically associated with PD, then I understand your conclusion.
As Terrific said above, if you do get a diagnosis of PD, do not think of it as the end to your normal life. I have had this disease 17 years now and am still leading my usual life! Medications are very effective now; exercise does a great deal for us; and a positive attitude helps even more. Although I am 68 and may not live long enough to see the cure, you at only 40 are quite likely to. (That is if you even have Parkinson's.)
I wish you good luck in dealing with all the fuss over the holiday weekend. I think if I were in your place, I would try to remain detached and calm, focussing on my own well-being rather than socialising. Maybe soon after that you can see a medical professional who can determine positively whether you have PD. Just not knowing is probably contributing to your anxiety and tendency toward depression.
Sincere best wishes,