Why do your feet fall asleep, and is it dangerous?

The medical term is paresthesia. Sustained pressure on a nerve, from sitting cross-legged, kneeling, or resting an arm over a chair back, compresses it and disrupts its ability to transmit signals, producing first numbness and then, as pressure is relieved and the nerve resumes firing, the disorganized burst of sensation felt as pins and needles. Circulation contributes but is not the main event: the common belief that the limb has been cut off from blood supply overstates it, since nerve compression alone accounts for the sequence and its timing.

The recovery sensation is unpleasant and self-limiting, typically resolving within minutes as normal signaling is restored. Moving the limb, changing position, and gentle movement speed it. There is nothing to be done to prevent the sensation once compression has occurred, and it is not causing damage in the short term, though sustained compression over hours, as can happen with intoxication or immobility, can cause genuine nerve injury.

What warrants attention is a different pattern. Numbness or tingling that occurs without an obvious position, that is persistent rather than transient, that follows a specific distribution such as one side of the body, that comes with weakness, or that progresses over time deserves medical evaluation. Peripheral neuropathy has many causes including diabetes, which is the most common, along with vitamin B12 deficiency, thyroid disease, alcohol use, certain medications including some chemotherapy agents, and nerve compression syndromes such as carpal tunnel. Sudden numbness on one side of the body, especially with facial droop, weakness, or speech difficulty, is a stroke pattern and is an emergency requiring immediate care rather than observation.