I can only reiterate what the above poster has said - your feelings of calm are indicative of a simple chemical reaction - it needn't imply a propensity towards enjoying or being unable to overcome this sort of thing. Self harm also takes different forms - it doesn't always include the dramatic scenes depicted in film or online.

Help for young people outside of strict parental authority isn't impossible - there are hotlines, guidance forums, support groups, school counselors, you can also ask your doctor for advice.

Please know that what you're going through is very common - the important thing is that you recognize it's a problem and you want help. That is essential for recovery.