Quitting was pretty mild for me, but my habit didn't go up to 1 pack a day until about 10 years ago or so (for many years I was about 1/2 pack a day). I did cough up some stuff, but nothing major. I had some chest/lung pains for the first few weeks as well, but those are passing. Since others have mentioned bodily functions, I also had constipation for the first week or so.
At the 1 week mark, I did hit the "taste wall" that hairball mentions (couldn't taste any vape at all for about 3 or 4 days, but could taste food and such). Even changing flavors didn't work for me... just had to work through it.
To make you aware, some people crave the "whole tobacco alkaloids" (WTAs) that are in cigarettes and not in vape. I'm obviously one of those, because at about 2 weeks, I had 2 or 3 bouts of really bad analog cravings even after chain-vaping 24mg juice. They lasted for several hours each but eventually passed (I did NOT cave to them). I feel that's all behind me now.
I'll also second the recommendation for a high nic juice (24mg is probably good) for your first juice... technique is different with vaping, and many people treat it like a cigarette at first which doesn't work. Read the 4 part beginners tutorial on technique. Once you figure it out, 24mg may make you whoosey... at which point you can drop it down.
Hope this helps... good luck!