I will wade in here with a little opinion of my own because I know what you mean when it comes to post-opiate anxiety. I think one of the reasons I liked opiates so much is because my natural state is an anxious one. I have a therapist who says people are basically either depressive or anxious (sometimes both) but those are the two hemispheres of the human condition.
Without the opiates, the natural anxiety remerged for me (although the opiates had started to make the anxiety a problem as well). But, I have found that Buspar and a low dosage of clonazepam (a benzo, I know, and not a long-term viable option) have helped me channel my native anxiety into the motivation to get things done. What I mean is, I try to think of my anxiety as my natural state and the thing that gets me out of bed and helps me tackle the problems of the day. However, when it gets debilitating then it can overwhelm you and walking the line between anxiety as a motivator and anxiety as chain around your neck is not an easy one. But, I think it is a line that a lot of people who don't have issues with opiate manage.
You know? I think it is your subconscious' way of say "Get up Jack, you got some stuff to do" and that is good. But, when it turns to fruitless worry then it can easily pitch you right back down the whole of opiates or booze or whatever.
No question about it, opiate withdrawal will bring on high and unhelpful levels of anxiety but one day in your future you may find that that anxiety becomes manageable and actually is a motivating force in your life.
My advice would be to go do something that you know if causing you anxiety, I don't know what it is... balance the checkbook, clean the bathroom, call a person you have been avoiding, make a household budget, teach the parrot to quote Chaucer, slip your toe nails, whatever. All the opiate withdrawal issues aside, anxiety is often there for a reason and if you can start to address those reasons in a sober and methodical manner you may find the level of anxiety becomes a lot more tolerable. Time heals all things but so does getting s**t done.
Best of luck!