I'd read somewhere that massaging your inner sphincter (read fingering) was a good way to calm the spasms by helping the blood flow more in that area. At first when I started doing it (with KY before every BM) it hurt a bit and I could feel (for the first time) my inner sphincter spasming. However now that I do it all the time, I can't feel any sort of spasm and I feel barely any pain at all. So I think a mix of lubing up the anal canal and deep massaging is really helpful. Still not sure I won't find myself screaming for my life again one day, but I think I'm well on my way there.
Has anything like that happened to any of you?
N.B. Being gay, I was already used to having a finger up there, but for those of you who have never done anything like that, here's a non exhaustive list of things to keep in mind when massaging your inner sphincter:
1. Use a lot of lube
2. Go at your own pace, it's not a race to get your finger to the inner sphincter, so don't ram it in. Think of it as any other kind of massage, you wanna be gentle with your anus (but you probably already know that

3. Take the time to find the right angle. Twist your finger around until you feel really comfortable. If it hurts, try another angle.
4. Make sure to cut your fingernails, they can be a pain and can probably make your fissure worse off.
5. If you're a man (I don't know much about women sorry), really take the time to find your P-spot (as I like to call it), otherwise known as your prostate. Doing so is the best way to achieve total relaxation.
6. Don't forget to wash up afterwards.
I hope at least one person will benefit from this "guide" :) All our bodies are different and react differently to stimuli, but give it a try and it might help save your butt!