Testicle went inside me?!

Normal, most guys can fully retract one or both testicles, most commonly occurs when a guy is lying on his back. The testicles retract on their own especially when aroused, and can easily slip back into the depressions where they dropped from. Not a problem as long as you can easily finger it out, and when getting ready to ejaculate both may be fully retracted. You are fine dude.

Entirely possible here. There are two "tubes" on either side of the pelvis that your testicles descended through just prior to birth. When they are developing, they are actually up just under the kidneys (very similar to the female ovaries in position. After they descend, the tubes usually shrink down and only allow the passage of blood vessels, nerves, and the vas deferens to the area around the prostate. Some people have this though where the tubes don't shrink as much, causing the testicle to slip back up into the abdomen, or more commonly, for the intestines to slip down into the scrotum (inguinal hernia, what they are looking for when you turn your head and cough). If this is truly happening to you, while it's not dangerous or painful to you right now, it could put you at severe risk in the future for a hernia. See your doctor and check out your options.

Trust me, you do not want to see your scrotum the size of a basketball due to being filled with your intestines. I've seen it, and it wasn't pretty.

X-Ray/CT Tech

thanks god this is literally impossible because of the muscles in your pelvic bone also you have several glands and transportation tubes down there so they would have to snap for this to be possible. that would cause internal bleeding then death and a terrible terrible pain. good job trolling though i bet you fooled some people ignorant enough out there

It happens often to me too, it's normal, happens when you suck your stomach in.
Don't worry about it.

Did you let em' finish? how did he manage to get it up their far enough for his balls to fit to? you is one freeeeaky bro!