Hi I Had Been On Cymbalta For About 9 Years

Hi I had been on Cymbalta for about 9 years for chronic back pain and had been weening myself off of it over the last year because I am concerned about long term use. I had weened myself down to about 10 mg or less. Wednesday 1/2 weeks ago I experienced some debilitating back pain and dealt with about a week and then became concerned that I should start back on the cymbalta because I need to be able to work. I started on 20mg on Thursday night and have sense lost my appetite and have no motivation. I've had to fight to get out of bed. I don't recall experiencing this when I initially started cymbalta but maybe that is because I had been on Effexor before switching to Cymbalta. Since I was not completely off I'm wondering if this is just a side effect of bumping the dose up and how long can I expect this to last and will I need to go all the way back up to 60mg to not feel this depressing feeling and to get my appetite back?