allergies
"I started taking Xyzal after a single episode of urticaria.  I have had hands tremors for 40 years, severe enough to interfere with my work as a nurse.  After 2 days, I noticed that the tremors were gone.  To verify it was linked to the medication, I stopped taking it, and after 2 days, my left hand started shaking again, so I restarted it.  It's been 3 weeks, and I am still free of any tremors."