Do your best to act like you are hiding the tears, and maybe they will get the hint that you don't wish to discuss them?? I know with myelopathy (and MS) it is very common for tears to begin to roll down our faces...often for "no reason" (of course there's always a reason, but maybe just medical?) The thing with MS groups though, we ALL know and understand and don't need to "discuss" anything!
Just tell them it happens sometimes.

(((hugs)))