Here is my experience with the Alien Hand Syndrome; I was lying on the couch in the middle of the afternoon and soon fell into a deep sleep. My head was resting on my arm, my hand hung around behind my neck over my cheek.
I woke up an hour later and when I opened my eyes I saw a hand above me. It looked like someone was reaching at me. The more I moved away, the hand followed, hanging limp in my face. Was someone behind me? I sprang to my feet startled, afraid I was about to be strangled by this hand. After a few seconds I realized it to be my own hand.
My arm had fallen asleep, so I couldn't feel it. That's it! Some experience, eh! Here's another;
The Alien Hand Syndrome
Dr. Goldstein was the first person to record this phenomenon. The woman wasn't the first he'd had experience with and wouldn't be the last. In 1972, it was officially recognized as a legitimate disease, Alien Hand Syndrome (AHS). The majority of cases are the side effect of brain damage due to an operation on the brain called corpus callosotomy to relieve epilepsy. Other causes could be; head traumas, strokes, aneurysms, tumors, and an assortment of degenerative diseases, like Alzheimer's.
Some people believe the hand is not theirs, they assign it a name, try to reason with it, punish it. They attribute it to ghosts or demons.
Luckily, it's only active when awake, or who knows what might happen. Many an alien hand have been implicated in many crimes; shop lifting, petty theft, removing of clothes in public, masturbating in public, car accidents when the hand pulls the steering wheel away from the other hand, etc.
Since the discovery of this disease in 1908, there have only been a handful of cases, about 50 have been confirmed. Many other Alien Hands have gone undiagnosed, or written off as some other psychiatric disorder.
However, a rogue Alien Hand, someplace, somewhere is threatening it's owner with strangulation. I hope it isn't you. There's only one solution.
Further Reading: Alien Hand Syndrome and Other Too-Weird-Not-To-Be-True Stories