I purchased 024 and used this morning because I was hurting badly in my shoulders and my whole back. The pain did go away, but I am left with a tingling sensation radiating all over my back and shoulders down into my leg. I called my son who is in med school and he said it sounds like referred pain to the nerves, but he didn't think it was anything to be too concerned about unless I had a lot of weakness or numbness. I was just wondering if anyone else has had this problems using 024. It actually feels like I am using the TENS unit with the electrical stimulation without the unit.