Debating staying on Xanax for a month or starting Cymbalta?

I have anxiety and panic attacks in relation to pain, and I'm recovering from a back injury that happened at the chiropractor's office while I was getting a different issue fixed. Chronic upper back spasms and daily all day headaches. I find if I take a xanax (.25 usually) my muscles relax and I feel much better overall - taking less advil, etc. But this has been going on for a couple of months so my dr. prescribed Cymbalta. Of course, being anxious about taking anything new (I typically am very sensitive to meds and puke on antibiotics, etc) I did my research and now I'm afraid to take it.

My dr. doesn't get any kickbacks from pharma and really thinks this can help stop the viscious cycle of anxiety and back pain so I can heal once and for all (and go back to occassaionl xanax use once every few months for situational panic attacks).

My biggest concerns are:

1) I have a major deadline for work in the next 2 weeks - I can't afford any set backs from side effects if they happen. My husband and I also have an extremely rare (years since last one) weekend alone together in a few weeks.

2) I'm concerned about signing up for a med long term (dr. said 9 months) and the withdrawal from it (though I'm certain to have bad withdrawal from xanax as well).

My question is really just to get people's opinons on if I should hold off a couple weeks and stay on xanax daily and then go to cymbalta or go ahead and start cymbalta now? My. dr is confident I will tolerate it well and it will really help me since I've been having panic attacks and significant anxiety daily for the last few months that is hurting my progress of healing. He said it's my discretion when to start. My Rx is 60mg once daily Cymbalta. I have xanax in .5 and .25 forms. 

Am I being silly overthiking it (the irony of being anxious about taking an anti-anxiety med), the answer to better health could be right here on the counter? I've never taken an SSRI or SSNRI before and am not depressed. I've tried Buspar once and cried all day and was completely out of it.