I had an emp a while back that did not drag its tail until a couple hours before it died. It must have been ill upon arrival because I only had it for about 2 days (and the stinger part of his telson was missing/broken upon arrival as well).
This time around I purchased my emp from Petco instead of having it shipped. I'm still watching the scorp like a hawk because it is still new and that last experience was a bit traumatic for me. Fingers crossed!
Your scorp seems to be ok though, I cannot see any abnormal bumps or spots from the picture.