Sixbuckets...influenza is just a blanket term. The one that killed so many people was spanish flu. There are many other types of fluenzas out there....my favorite being "afluenza" which only killed four people.
It is why you get a different flu shot every year because the virus changes. It is kinda like the difference between a northern gray squirrel and a southern ground squirrel. They are both squirrels and they have a very common ancestry, but they are slightly different. So like the virus has a family tree where some versions are crazy infectious and can kill the elderly and infants, and others are very mild and not very infectious. The reason you don't keep getting the same flu is because of antibodies that your body builds up. Antibodies are kinda like the vaccine to that specific strain of virus. If you have had that version, your body will fight it off easily, however if it mutates your flocked. Here is an example. I have had an immunization to hep b. I have those antibodies in my system. Whenever I get a blood test they are there, and will always be there....unless I get some crazy immuno deficiency problem going on at some point.
So to answer the question opiate withdrawal is like some crazy version of the flu that causes different effects in everyone however it is extremely baffling in the fact that it makes you suffer profound emotional problems throughout its duration and months after. Consider having the flu and then finding out your cat burned down your house with your prized collection of rare spoons inside after your wife left you to be with your brother who also was renting the house that burned down so he made of with your woman, your home, your cat, and probably your spoons. Wow I am really rambling...lets just leave it at opiate withdrawal really sucks.
Sounds like a country song, no?
I haven't used H, so no first hand experience. I did nurse someone through morphine withdrawals, and from what I saw, this is an accurate description. I've seen posts that lower level opiods/opiates, such as codeine, kratom and hydrocodone produce lesser withdrawals. From what I've observed, they all suck.