Oh please help me i am scared

Okay, before i ask my question please think in the vein of the movie the sixth sense- no i do not see dead people but a strange occurrence happened to me in which i received bodily harm from no apparent source.

Okay so this one day about half a year ago i woke up with these strange dark purple streaks across my back. They were really long and for some stupid reason i thought that it was just my genetics being cruel and worsening my skin condition as some kind of joke- well as it turns out...

They were actually scars. Yesterday i showed them to my mom and she was noticeably alarmed. She ran her fingers over them and said that there was a definite indentation and they were definitely scars. She actually asked me if i had been harming myself out of emotional stress or something.

These scars are too bad to be made by a back pack or any other thing that i routinely carry on my back, they are not stretch marks as i am very thin (at first i thought it may be from a growth spurt but i think i stopped growing a while ago (i am sixteen) and they appeared after the fact)

This is really strange for me, i have never harmed myself and have never consciously sustained an injury this bad (it is really bad they run up and down my whole spine)

please help, my mind keeps trying to make me think that something spooky (supernatural) caused it.

To be totally honest... they sound like stretch marks. I have TERRIBLE stretch marks from my medical condition that occurred suddenly and look horrible, the theory being that they are worse than normal stretch marks because of high cortisol levels. I also have scars from a self harm addiction I battled for many years. Scars are raised, not indented, I don't know that I've ever encountered an INDENTED /scar/. Stretch marks however commonly are, and it seriously sounds as though that is EXACTLY what your issue is. And despite what you may believe, with the right conditions they can appear pretty much overweight. And also despite popular belief stretch marks don't necessarily only occur with rapid weight gain, but often with hormonal imbalances that don't cause a noticeable gain in weight (how this happens, I don't know, but my weight has been stable for quite a bit, and seeing as I'm still ill, I STILL wake up every now and then with completely new stretch marks, and there are people I know who have the same issue. They aren't necessarily fat or gaining weight, either.) So really, as much as you may like to believe they're not, they sound exactly like stretch marks and unlike any /scar/ I've ever seen.That's the most simple explanation, and so likely your issue. Particularly since hormones play a huge part, and being a teenager you're going to have those types of fluctuations.