Am I having a SSRI withdrawal?

So my doctor took me off of Lexapro about a week and a half ago and out of nowhere 2 days ago I started getting brain zaps or this feeling like I'm falling or dropping for a split second . It seems to only really happen when I stand up plus I get so dizzy and disoriented and short of breath and I get really bad tremors.I've already been checked for everything that you could possibly think of blood test, EKG , ultrasound ,CT scans . You name it I've been tested and no one can figure out what's wrong with me . Any ideas ?