I don't SI so feel free to blow me off

From my understanding SI causes the body to release endorphins which is what really causes the calm after. Our bodies can get addicted to the endorphins though just as they could a drug not created by the body. Exercise is a great alternative as it too releases endorphins. My guess though is that your body is going through a withdrawal of sorts from the endorphin rush... which is what leaves you wondering "what if this stops working". Breaking the cycle is really, really hard as our bodies will want to pull us back to equilibrium even if it isn't a healthy one.
Hang in there. You CAN beat this!!!!