Panic Attacks Support Group
A panic attack is a period of intense fear or discomfort, typically with an abrupt onset and usually lasting no more than thirty minutes. Symptoms include trembling, shortness of breath, heart palpitations, sweating, nausea, dizziness, hyperventilation, and sensations of choking or smothering. Panic attacks can be very sudden, appear to be unprovoked, and are often...

ask a pharmacist for the dose range for lexapro and consider upping the dose, this may get it working again, you might also augment it with another med such as buspar but this is uncertain and a bit of a black art
if still no help, try an antidepressant of a different type, there are several, lex is a prozac type, valium will help in the short term, the usual cautions when driving apply of course
let us know how things work out