I've been reading on here for the past 6 months when my fissure wouldnt heal, and I didnt quite understand why, as they had always healed within a couple days in the past. I tried a bunch of things, but after a few weeks found that Magnesium (Mg) was the best, although occasionally it would result in 3-4 trips to the bathroom the next day...but at least it didnt hurt. Constipation has never been my problem, but hard stools resulting from lack of water and possibly lack of fiber and overdoses of stress.
Like many of you, you feel healed after a few weeks, start to get complacent, then BAM. Fissure returns. I finally decided to go see a CRS and got nitroglcyerin ointment. He told me to ease off the Mg and add fiber (psyllium). This was the interesting thing he told me. He said that if I continued having runny poops on the Magnesium, my sphincter muscle (cant remember which) will not be able to expand as much as it had before -- I guess it begins to atrophy. He said adding fiber would help restore the muscle's function and so once I was healed, I'd be able to pass normal BMs once again without tears -- whereas if I constantly used Mg and then stopped suddenly, I would probably get a tear because my muscle wouldnt be able to expand to handle it (he did a nice demo of the spincter muscles and anal canal by opening and closing his fists). He said I could slowly add fiber and wean myself off Mg (I was taking 1000 mg/day at this point)...and he said my sphincter muscle wasnt "that bad" and not something he would consider requiring surgical. My fissure had almost healed at this point and I wasnt in pain, so I felt pretty good and relieved after seeing the CRS finally. (Word of advice: Go see a CRS. I wish I had done this back in the trial and error phase in the first few weeks). I felt I didnt even need the ointment at this point, and used it only for a couple days then went about my pain free way for 3 weeks.
I followed the CRS' advice, afraid that I would always need a huge dose of Mg and possibly loose stools for the rest of my life if I didnt add more bulk to my stool. Added only about 1 tsp of metamucil a day first, then 1 tsp in the morning and 1 in the pm. I eventually got down to about 500 mg Mg a day with the fiber and was impressed by my poops, the way only people with a fissure can look triumphantly at their poop when they have a pain-free BM.
But one day I upped my fiber content (at this point i had used up my metamucil and switched to psyllium pills from Costco, so I was taking about 9 g of fiber pills a day (half in am and half in pm)) and didnt drink enough water. I got complacent and even drank coffee that day. I took Mg as usual, but I think the culprit was not drinking enough water. It wasnt a full blown pass out from the pain kind of tears I'd had earlier this year, but it was enough for some blood and panic. I kept up my fiber regimen and stepped up my Mg again, and even added a dose of good old miralax just for the hell of it. Started using the ointment again, too. Headaches

The 2nd day of the recurring fissure -- again another bulky poop to start with (it wasnt overly hard, but not soft and clean like the days of yore), followed by the deluge resulting from the Miralax and Magnesium...they dont call it "the runs" for nothing! I had a lot of water the previous day along with the Mg and Mlax, so I was outraged on top of my pain that my poops were still well formed initially, perhaps the dreaded initial firmer plug that some people get (it was real, not just because my sphincter was tight). Fine then, I took 1500 Mg, determined to really make things soft and loose (I gave the miralax a break this time. Also noteworthy -- my CRS said it is fine to take Miralax daily everyday for those worried about that). I did a sitz bath, continued w/ ointment, drank water, about 8 g of fiber, lots of fruits and veggies...
So this morning was expecting nothing short of Niagara, only to have another relatively bulky difficult passage resulting in minor pain, which I think I lessened considerably by assuming a semi-squatting position and vigorously jiggling my ass cheek and kind of moving my pelvis back and forth while still seated in a semi-squat -- yeah it sounds weird, but I think it helped and also it was a nice little 2 min cardio workout to keep a steady jiggle, almost like i was trying to push it along with my ass cheek. Then after I got to work, the waterypoopworks turned on from all the Mg, but even that poop seemed firmer and bigger than usual.
My only conclusion is that I was taking too much fiber. I generally eat healthy but go on occasional cheese binges, which also happened the day before the fissure returned. Perhaps I added too much bulk too fast. So whenm your CRS tells you to add fiber, dont go nutso with it like I started to do after 2-3 weeks. Especially if you already eat a decent amount (altho I think I probably dont come close to eating the recommended daily dose even tho I have a few servings of veggies/fruits a day usually).
Anyway, so I'm back on the path towards healing -- nitroglycerin cream, Mg, maybe Miralax if things get dicey, sitz baths, hot water bottles on my bum at night, and after reading here again am gonna try to lube the area before a BM with vaseline to see if that helps while the wound is healing. I am only taking 3 g psyllium a day now, as I dont want to risk the bulks. I am meeting with a naturopathic doctor in 4 days regarding this, too, since the CRS cant really help with nutritional advice and am wondering if there is some way to speed up healing with diet and even acupuncture? Havent looked into it, but thats the ND's job!
Best of luck to all of you and happy holidays. <3