it's hard to understand... but physical pain does help cover up emotional pain when it's that bad. or atleast it helps you forget about it for a little while.
I did it about every day for 2 years... stopping a year ago. i can't explain why i did it... i was just in a stage where i wasnt thinking straight. when you get very very deeply depressed you dont know what to do and you'd do anything to escape from that feeling. I dont even know what i was thinking... and it's something i'd NEVER do again, cause I know how bad it can get... you just keep going deeper down till you get help, luckily i got help in time.
but in any sense, self mutilation is NEVER the way to go... it just makes things worse and sometimes you can't tell till it's too late. and plus, once you start, it becomes an addiction that is hard to quit. it's a scary state to be in.