I'm scared, is this herx or failed lyme treatment?

Tonight I am a little scared.  For the past 2 months, I haven't had any of the weird neurological symptoms that started about 1 month into getting sick.  Since I started the Bicillin injections, I have gotten MUCH better, and great improvement started within 2 1/2 days of my frist injection. 

This past Tuesday evening, I felt great.  Don't get me wrong, I never feel free of Lyme, but great compared to how I have felt since I first got sick.  So I went out to dinner with my girlfriend Grecia & then even stopped off at the mall for some very minor Christmas shopping (this outing was a HUGE feat!).  I had some aches & pains, my back hurt, so I came home.  No big deal, I just thought I had worn down for the evening.  Happens often, even on my best day.  My neck started hurting & then the headache came. I haven't had that in about 2 mos!  Well, it's 3 days later & my neck is so stiff I can barely look left or right, the stiff neck has gotten worse.  My knees have also started giving out on me again when I walk & I am also off balance again.  These were also symptoms that have gone away since starting Bicillin.  Also, the cognitive brain stuff.  I can't find the right words for things & I am putting the wrong word in a sentence.  It's starting to bother me.  It's giving me anxiety.  Is this a herx reaction?  Or is my treatment failing?

I talked to my doc yesterday & mentioned about the neck pain.  She says if it's still there on Monday she is going to have to prescribe something strong.  She doesn't want me in pain because pain weakens your immune system.  I currently have a prescription for oral Ketamine & I have some in my medicine cabinet.  But I am afraid to take it.  There are possible psychadelic effects that I dont' have any interest in finding out about. 

Maybe this is a lyme cycle, but I hope it's a herx.  Because a herx is just the bacteria dying off & it means you are on the road to recovery.  My doc think's I am herxing.  I just hope she's right.  The neurological stuff is hard to deal with.  I can handle pain, but I can't handle the scary stuff.