Everyone is different...but I also think the settings matter and where you place the electrodes is important too. I'm no expert and can only speak about my own experiences though. I do know some people don't respond well to TENS and then there was one person I spoke to who had a bad reaction to TENS but then changed the settings and it have her relief. I know for me too I also start at the lowest setting I can on the TENS and then bump it up throughout the treatment gradually as I tolerate the level I'm at. If you already had a bad reaction though I would make sure any future trials with one (if there are any) are done under the supervision of a physical therapist or doctor. Doesn't work for everyone but for me it was/is a life saver.