I usually smoke high-quality dank several times a day, every day, and I have been for nearly 6 months. Before that I smoked atleast once or twice nearly every day for about a year or two. I have stomach problems in the first place, as my stomach lining is ruined from constant caffeine abuse (possibly also from my ex amphetamine addiction). However, not smoking increases these symptoms to an almost unbearable level. Typing this now, I'm totally dry and have been for several days. My stomach has been in intense pain and almost every time I try to eat I get very sick to my stomach and have to take some sort of stomach medicine.
Cannabis CAN be physically addictive if you use it often enough. I also get mental symptoms, such as extreme irritability. For example, when I woke up this morning I got on the computer and tried to open too many things at once, so it froze, and I punched the monitor so hard that one of my knuckles got fucked up. After I had done it I thought about how stupid it was, but when I go a while without smoking I just overreact to things without thinking about it. However, unless I am high at the time, I am usually not lazy and don't find it hard to concentrate.
Some users don't smoke enough to get the withdrawal symptoms, and some just plain don't get them. Regular breaks and not ABUSING weed can stop them, however.