Try not to be afraid. Everyone reacts to meds differently, and some people will have bad reactions, and some will have fantastic results!
Your doctor is starting you on 5mg, which is safe & smart. This way you can see how you react to it.
I personally had a bad time with Lexapro, but I knew it within 3 days & simply stopped taking it (and had no problems after I stopped). So rest assured that you can just stop taking it if you don't like it
Good luck to you, I hope it really helps you.