There are many issues relating to anal fissure, hemorrhoids and other anorectal conditions. I can only speak of my experience and what I went through.
In my case, I had a large anal fissure that was exacerbated by prolapsed internal hemorrhoids. Any bowel movement would force the hemorrhoids out past the anal sphincter, where most of the pain receptors lie. This would in turn rip the fissure further, escalating the pain. The bowel movements themselves were excruciating, and the sheer intensity was intolerable. The pain would linger afterwards in a slightly dulled form, but after two hours another surge of pain would come back in a wave of terror that was simply unbearable and lasted for another eight hours.
In the case of anal fissure, the problem is the actual tear in the rectum. Every time you have a bowel movement it tears the wound open. It takes a day or two for the tear to heal, which is about the time when the next bowel movement comes, ripping it open again.
It is a vicious cycle, akin to the curse of Prometheus, whose constantly regenerating liver was eaten by an eagle every day.
It is common for a skin tag to develop around the edge of the fissure from the scab constantly forming and tearing again. In many ways, you can tell how bad the condition is or how long it has been going on by the length of the skin tag. In my case, when I went to see an anorectal doctor for a diagnosis, he immediately saw the skin tag and noted that it was a very severe case of anal fissure.
Internal hemorrhoids mainly have to do with circulation in the colorectal area. Essentially, there is stagnation in the blood flow and a lack of musculature in the pelvic floor. The tissue around the anal sphincter loses its elasticity, causing hemorrhoids to develop and sag.
In almost all cases, internal hemorrhoids start out painless – you will most likely not even know you have them. If you do feel them, it means they have already reached an extreme level that is very difficult to reverse. They have grown and sagged down so much that they are protruding past the dentate line – that interface where the anal sphincter regulates bowel movements and keeps them in or out.
Another condition is external hemorrhoids, where the hemorrhoids form below the dentate line. In most cases these hemorrhoids are not painful and just a nuisance. They will go away on their own.
However, some external hemorrhoids can be extremely painful, especially if they grow to a certain size, in which case they are called thrombosed external hemorrhoids. The way to cure the pain for this condition is very simple, and if you have thrombosed external hemorrhoids you can skip ahead to How to Treat Thrombosed External Hemorrhoids.