I'll tell you about my own experience first & see how it compares with everybody elses.
Day 1: No noticeable difference in my behaviour.
Day 2: Woke up from very bizzare nightmares about people throwing me off large cliff faces and trying to drown me in piss contaminated water. I started crying uncontrollably upon awaking. I checked the clock and saw that I had only slept 2 hours that night. Although I had been smoking 20/day I found myself feeling very SICK at the thought of having anymore tobacco. I got alot of exercise at this point walking here and there. If you dont have any family around to support you, this is the windowframe of time you need to use to pick up supplies. You might not realize it yet, but u are gonna feel like u are close to DEATH in 24 hours time. I remember by the evening time I was complaining that my chest felt tight almost like an elephant man was sitting on me and I was struggling to breathe. I desperately wanted to go to the hospital to get some oxygen, but decided against the idea because I didnt want to use the emergency services unless I felt it was completely unavoidable. In the end we walked to the hospital then when we got there I said I didnt feel like raising the alarm bells and we never even walked through the entrance and turned our backs on the place.
Day 3: Hardly slept at all last night. 30 minutes at most. It was another nightmare, this time about somebody trying to asassinate me. Woke up feeling sick as a dog. Feel very bed ridden though and almost unable to move. I keep feeling very sick and although I am trying to sleep, I wake up vomitting. The vomitting gets progressively worse until I almost asphxyiate on my own vomit by the time it is evening. I have heard stories about people dying like this. I am puking up bile once my stomach contents has been regurgitated. This is EXTREME hardcore! Puking up bile is not like being sick normally. It is extremely PHYSICALLY TAXING on the body.
Day 4: Completely unable to eat/drink because I will be sick. Nil by mouth! Lay in bed the whole time in a tunnel of insomnia unable to move but unable to sleep. Lots of aches and pains. This looks quite offensive to write, but you will struggle to get out of the bed to use the toilet because you are too ill. You have been constipated for MONTHS, now when u think u need a fart u actually have diarrohea and will literally shit urself a little. This is very sick. I am also too sick to brush my teeth for a few days which is very bad.
Day 5: Same as day 4. No food, no drink, no movement and no sleep. Lots of pain though. I can manage to take a shower but its a struggle to brush my teeth. To a normal person, not brushing their teeth is borne out of lazyness. Acute opiate WD is FORCED lazyness to the extreme. You quite literally cant help urself.
Day 6: After approximately 5 days I can manage a litre of pineapple juice without being sick. My insides are completely screwed though. I can manage a shower here and brush my teeth after days of plaque build-up. My insides are full of air where there should be food. I can manage icecream but dont feel like "solid" food yet. I keep belching and farting like some sort of depraved sicko. It's horrendous and quite disguisting but I am making this graphic account so that people interested can know what it is actually like. I dont often feel ashamed of my actions but I was very apoligetic to my mother who had to nurse me through these bad times even though she has a full-time job to contend with.
Day 7: I think this is where the recovery STARTS even though I am NOWHERE NEAR rehabilitated yet. I can manage to eat even though I was sick after overeating. I think I can manage about an hours sleep at night after about FIVE DAYS without a single winks sleep. That sounds like a hardened meth binge but the difference is I was in bed the whole time. I wasnt burning thousands of calories per day. This is a point that I dont think is given any credit when people talk about withdrawal from opiates. Total sleep deprivation occuring during the WD (tail-end) stage of "downers" and not from the acute actions of 'stimulants'. I put my fingers in my ears and scrape out what seems to be piles of ear wax. I also notice that my facial pores have become quite 'pussy' because I have not been washing daily for about a week.
I still havent smoked anything since going cold turkey from the fentanyl (unable to comment on the effex of street heroin though) and plan on quitting PERMANENTLY. Strangely, I have not even had the desire to smoke yet. My brain does not crave tobacco which was what kept me hooked since before I didnt have the strength of willpower to successfully QUIT. Just locking a smoker up in a cell cannot compare to the DEVASTATING PUNISHMENT of abruptly halting an addicts fentanyl supply pipeline. After enduring so much torture already, taking more opiates is completely out of the question for me now. ^Think about what I have just written, who in their right mind would want to return to that?? but my problem with smoking is a demon that I will continue to fight. The battle is not over yet. I managed one month without a single drag back in 2004, but I wasnt yet a hardened smoker at that stage. I realize now that the longer I can go without so much as a drag of smoke the better. It's such a filthy habit that I dont want to go back to "experimenting" with tobacco.
Heil JanSSen!
Kids will experiment, no doubt about it. And I think that if my kid is getting good grades and is respectful and responsible, I would probably be less concerned as well. 
