These may not be the most painful ways, but they have always been my favorite.
Strongly, with tiny, and close together stitches, sew sheets of leather together into a tube the length of your entire body, but several inches smaller in diameter. Soak the sewn tube in water for several days to increase its pliability. Equally, soak yourself constantly in a warm salt bath while consuming only water. Bring your tube to an open field, or to a tanning bed where you won t be disturbed. Attach a sturdy tether to your legs, arms or both, so you can not escape the area. Wriggle into the tube and remain in the light until you are squeezed like a tube of tooth paste.
Find or make a container that is taller than you are but wide enough you can t touch opposing sides. Set up a timed large scale grinding machine. Secure yourself to the bottom of the container in a way that toy won t be able to stand on top of anything that falls into the container. Grind double your weight of salt into a fine powder and have it poor in on top of and around you. You may also choose to mix in hundreds of razor blades and or exacto blades for your struggling pleasure.
This one s a bit more involved. Break a lot of light bulbs, and retain the glass shards (about 3 cups worth). Obtain about 3 cups of rock salt, and some beach sand. Mix the three together. This is where it becomes difficult and may require someone else s assistance so you don t just die of exsanguination ; find a way to get a nipple down epidural. Prop yourself up so you will be able to reach your pelvis without much flexing to cut yourself open from diaphragm to pelvis, or have someone do this for you. While lifting and moving your intestines and other organs around, pour in the owie mixture. And sew yourself up using small, close stiches.
If this is too difficult, men do this same procedure to your scrotum while it is fully numbed. Gals, your inner thighs will work in this case but the numbing can be more difficult. Make sure to immobilize yourself in some way shortly afterward so you can t rip your flesh off. Either way death will be slow and painful.
The old fashioned rat torture technique would be very painful as well. The use of incubator or heat lamps would be a simple source for intense heat. Getting a hold of the rates on the other hand could be a problem since they aren t as prevalent as they used to be and it is just mean to do that to an animal.
Roasting yourself alive in a large metal stove, pot, 50 gallon barrel or other vessel or just burning yourself alive would be excruciating.
Over all, pick your favorite mid-evil torture method, work in safe guards to keep you from escaping the pain, and eliminate the possibility for an interruption.