Katietrombone, I know exactly how you feel, that pressure with pain was not fun when my fissure was fresh, one year later and my fissure healed I still worry about having to use the toilet in a public place, because I still keep a routine.
I remember that the pressure went away once I got the nitro cream to ease the spams, so is a relation between the spams and the pressure and feeling of having to go all the time.
You think is going to last forever but thankfully it does goes away, mine was completely gone by month 4, but the pain and irritation plus set backs lasted longer than that, by month 6 I was more in control of the fissure.
My fissure was chronic but is gone for now, I know that it could comeback any time as that is the way with fissures, specially when I healed naturally.
Yes fissures can heal even chronic but we need some help to achieve that.
If I ever get the fissure to become as painful as it was during my first months of the fissure been fresh I would have not problem getting surgery, because I already know how devastating it can be to wait.