Not so odd Em, been used for pain relief for quite some time.
Many drugs have different uses and there are other anti-depressant medications used to assist with pain relief, to help get better sleep etc...
My gastroenterologist had me back on it a few years back. I most recently had it mentioned by my rhumatologist for fibromyalgia pain and lack of sleep but as I have problems with really dry eyes and mouth (from arthritis and suspected Sjogrens Syndrome) and it can make dryness worse so I went back on citalopram to help with that and am now on pregabalin.