To the best of my knowledge there is a valve within the brain that releases serotonin into the bloodstream. Ms can damage that bit of the brain leading to low serotonin levels. My neurologist said if you walk down the high Street one in ten people you see will be on serotonin inhibitors (antidepressants) and most of them don't even have MS! Dr Aaron boster does a good YouTube video on this topic he too has suffered to depression and believes there's nothing to be ashamed about by taking such medications. In my opinion it's principally the same as taking HRT which again is not frowned upon. Alternatively you can do a self referral for NHS funded CBT in most counties.