Yep, it's a sin. Who exactly are we to believe we have the right to damage god's creation? We are nothing! I witnessed 3 singh's drown a few years back, it should only make you stronger in your Sikhi, the realisation of death should strike you hard and help you to know that we do not have much time left in this life, we cannot afford to waste it... But self harm is no excuse for anything whatsoever, it gains nothing at all and loses so so much...
ismrhu ismrhu swis swis mq iblm kryh ]
simarahu simarahu saas saas math bilam karaeh ||
Meditate, meditate in remembrance with each and every breath - do not delay!
Coif pRpMcu pRB isau rchu qij kUVy nyh ]2]
shhodd prapa(n)ch prabh sio rachahu thaj koorrae naeh ||2||
Renounce worldly affairs, and merge yourself into God; forsake false loves. ||2||
Vaaheguroo!