The anxious feeling is your addiction speaking, telling you lies again, lies like 'if you have just one more pill, these feelings will go away, you know what to do'. Am I close?
That voice will tell you to go back to using, to give up again, to turn around and start that slow walk downhill to darkness. That voice is not you, and it has no power over you anymore. You know the only way forward is through. It gets easier, it gets brighter, it gets more beautiful each day. And yes, it does get better.