Lyric discussion by jdawg08 

Cover art for sickness lyrics by Superjoint Ritual

I think that he's talking about addiction, detox, rehab and how that stuff will kill you. The last two lines are the most telling "the sickness that saved us is killing us now". You turn to the drugs for escape, to help relieve the pain and then they take over and, if you're not careful, will kill you.