Lexapro quit on me

Hi All,

Well it looks like lexapro has quit on me. I switched from mirtazapine to lexapro about 3 months ago. Started at 10mg and did that for 2 months. Was feeling pretty reasonable, not great but not horrible. So a month ago my P-doc and I decided to go up 5mg to 15. about a week in, I started feeling better, felt like my old self for the first time in forever. That lasted about 2 weeks, then last Friday I woke up feeling really anxious. It's been downhill since then.
Now I'm anxious all day, no appetite, pounding heart, shortness of breath and insomnia is worse. Even fighting agoraphobia for the first time in a couple years.
At my last appointment we had talked about possibly switching to amitriptyline, so I emailed him this morning. I imagine I will start the switch tonight.
Anybody experience breakthrough anxiety like that? I've gotta assume after feeling so good to then feel so much worse for 5 days that it had to have quit on me.
Does anybody have experience with amitriptyline (Elavil)?
Any thoughts would be appreciated. I feel so discouraged.
Thanks.

Thanks SC.
I picked up the new prescription last night. Haven't started the change yet, though. I felt a little better last night, so I thought I'd give it a couple days. I felt so good for a while there that I don't want to give up on it too early. I'll give it a couple more days, I guess.