I'm so sorry to hear you don't feel well. I hope things are better today.
I would try to call the neuro and if you don't get through there, then call the Tysabri nurse and tell her what is happening.
Even if you do go in for the infusion, you will get some attention when she goes through the pre-infusion checklist and she will more than likely call your neuro for instructions as to what to do, when she finds out how bad off you are.
Good Luck! Please let us know how it goes!