I don't usually have cramps with enemas, but I do often have something similar: intensely pleasurable, explosive expulsions with very strong, almost violent, rhythmic contractions of my colon and abdominal muscles that can expel an entire gallon almost completely in a few seconds. When one of these starts, it's completely involuntary. I can't stop it, and I wouldn't want to because it feels so good, almost like a different kind of orgasm. I grunt involuntarily too, probably from my convulsing colon pushing up on my diaphragm. My whole body seems to convulse along with my colon. This doesn't work well for toilet expulsions, which is one reason I prefer bathtub expulsions on my back, (with a good clean up with bleach after the fun.)
I've got an extreme homemade enema rig that reliably produces these intensely pleasurable, explosive expulsions. I connected a one-inch diameter vinyl hose to a 5-gallon camp shower bag. I drilled a one inch hole through a 2.5" butt plug to make a retention nozzle for the other end of the hose, and I put a 1" hose valve in the middle. After I'm cleaned out, I fill the bag with water as hot as I can stand, open the valve, and inject a gallon of hot water to fill my colon in seconds. The shock of this almost always triggers a instant convulsive, explosive expulsion. These are so pleasurable that I sometimes can't help doing as many as 20 of these back to back. With the super-fast flow rate, and only needing to refill the bag every 5th enema, 20 intense expulsions don't take long.
After a series of convulsive expulsions, I experience amazing anal relaxation, an intense anal homeyness, and a deep hunger for extreme anal toys that makes anally-induced orgasm certain. I have a big toy ready on the side of the tub. Lately it's been a fairly stiff, 2.75-inch-diameter, 24-inch-long double dong. I pin one end of it down at the front of the tub with a 30-lb dumbell (also placed next to the tub.) I lube my anus, my entire butt, and the other end of the huge dong. I center my anus over the end of the dildo and push off the back of the tub with my hands to drive my butt forward. The fat dildo easily slides 6 or 7 inches into me up to my inner sphincter. I push a little harder, and the dildo penetrates my inner sphincter and goes in 6 or 7 more inches into my sigmoid. Then I start pushing off with my hands and feet to slide my slippery butt up and down the tub to fuck myself with a full 12 to 14 inches of dildo. I can't describe how good this feels. A mind-blowing, anally-induced orgasm is certain in the next few minutes. If I can control myself and keep both hands on the back or the tub, it can be totally hands free.
You should try it.