If you've previously had a habit, it doesn't take much for the withdrawal symptoms to come back. You might not be using enough to develop a true dependency, but I'm sure that once you've been through a habit it doesn't take much for your brain to go back to its old ways. It takes a very long time for your brain to go back to its pristine opiate free state after you kick, and for even years afterwards physical dependency can come back much quicker than it took to appear in the first place. Maybe after getting a taste of those devilishly heavenly opiates your brain is going back to junkie mode just enough to cause you to get some mild withdrawal symptoms. It took my years of using opiates on a regular basis recreationaly to build a habit which left me "dopesick" as we all know it, but looking back I can see the early signs of physical dependence as my usage increased. It was usually little things like sleepless nights, feeling a bit anxious and uncomfortable during the day, or sensitivity to temperature along with fluctuations of my own body temp. Things I could only wish were my symptoms as my habit got further along, but at the time were just enough to fool me in to taking more opiates to deal with the discomfort.
Another problem could be psychological cravings for the drug manifesting themselves in physical ways. It's amazing how much of an effect the mind can have on the body, which for me personally has been enough to make me feel a lot of the symptoms of physical withdrawal; ie. a flu reminding me of the feeling of dopesickness causing cravings which led to the sort of restlessness and anxiety symptoms one would expect during physical withdrawal during a period in which I was completely clean for months (I even got the watery eyes and constant yawning well beyond what one would experience with the common flu). You mentioned that you we're "relieved while waiting for the next hit". Becoming psychologically addicted to a substance usually occurs much earlier than the actual physical dependence. So while you might not have a full on habit, it still sounds like you are in a sense, "addicted".
For a recovering addict, occasional use is usually not an option and generally not a great idea. I know a lot of junkies and I've never personally seen chipping work out good for any of them. All of them eventually developed another habit and ended up back and square one, or realized what was happening to them and got out for good while they still could. I've seen a few people on the internet who claim to be successful in chipping as a recovering addict, but I think a lot of those people are either simply in denial that they developed a new habit, in the early stages of developing a new one, or super human beings who give the finger to their mind and body and win every time. These successful chippers win the lottery every time they play and never meet a girl/boy who didn't want to fuck them. I guess the benchmark for successful chipping would be if you can use opiates similar to the way I use marijuana these days. Every now and then I might buy a little bit of green and get high, or if some friends are passing a bowl around I might get in on it, but I really couldn't care less if I smoke or not and the thought rarely every crosses my mind. If it's presented to me and I'm not in the mood or have some responsibility I have to attend to later I have no problem letting the bowl pass me by. If its something where you use every three days or something and those three days are just a drag until you get your fix or if it really sucks if you miss whatever specific time you use and you make sure you get it as soon as possible you're probably already halfway back to a raging habit.
I'm not trying to preach here, but I can't stress enough that chipping after beating a habit is not a very good idea. Very few people manage it successfully and chances are very slim that you are one of those people. They are the same people that really can "quit anytime they want too", the kind of people who got their habit almost because they wanted it and laugh in the face of withdrawal. I'm serious here too, the kind of people who have so much self control that when they kick they just stop and deal with the withdrawal like a non-addict would deal with any other illness. Somehow they manage to have enough willpower to beat the odds afterwards and use their previous master in moderation. Either that or they we're never addicted in the first place and always have been moderate with their use. I honestly just don't understand how people do it. Maybe I'm a successful chipper, I've been using "just one last time" for the last 10 years. I've always made sure to moderate my usage and space it out in such a way that I only use once my previous dose has worn off.
