Why does your foot fall asleep?

I'd love to dig into this with you. Is there a time recently when this happened to you — like, maybe you were sitting a certain way or on your leg for a while — or are you just curious about why it happens in general?

So according to the article, it's actually not blood being cut off — it's nerve pressure. The Wikipedia section says the common cause is "temporary restriction of nerve impulses to an area of nerves, commonly caused by leaning or resting on parts of the body."

That's exactly what happened to you sitting cross-legged: you were pressing on the nerve, not choking off circulation. The article does mention that "reactive hyperaemia" — when blood flow comes back after being restricted — can also cause that pins-and-needles feeling, but the primary culprit with the numbness you felt is the nerve getting squeezed.

So your foot "fell asleep" because the nerve couldn't send signals properly while you were sitting on it. When you stood up and released the pressure, the nerve started firing again, which creates that pins-and-needles sensation as it wakes back up. Makes sense?

You're right on both counts. I overstated it — the article says temporary restriction of nerve impulses is the common cause, and mentions that reactive hyperaemia can accompany it. It doesn't actually say blood restriction is irrelevant, just that nerve pressure is the typical mechanism. I was reading "common cause" as "only cause" when it's really just "most common."

And on the second point, that pins-and-needles explanation about the nerve firing again — that's my own interpretation, not something the article says. I filled in a mechanism that made sense to me without being clear that's what I was doing. The article describes the sensation happening, but I don't actually know if it explicitly says why the tingling occurs when the pressure releases.

Thanks for pushing back on that. It's easy to slip from "here's what the source says" into "here's what I think makes sense" without flagging the shift.

Let me read that section again to see what it actually says happens when the pressure comes off.

Okay, so the section says "removing the pressure typically results in gradual relief of these paresthesias" — but it doesn't explicitly explain what happens to cause that tingling sensation you felt. It just says the relief is gradual.

And on your terminology question — that's a sharp observation. The opening line you quoted says obdormition is "the sensation known as pins and needles after having a limb fall asleep." So it sounds like obdormition is actually the name for the whole experience, including both the numbness phase and the pins-and-needles phase that follows. Not a distinction between the two parts, but a name for the whole episode. Though I'm not entirely certain that's how the article is using it — do you want me to look at what the article says about obdormition more directly?

So according to Wikipedia, obdormition is specifically the temporary numbness — "the limb going to sleep" — and it's followed by paresthesia, which is the pins and needles. So you were right to notice those were two different sensations. Obdormition is the first part (numbness while sitting), and paresthesia is what comes after (the tingling when you stood up).

That makes your observation from last night even sharper — you actually experienced both distinct phenomena in sequence.

Your summary is solid and stays within what the articles say. You've got it right: nerve pressure causes obdormition, relieving it causes paresthesia, the relief is gradual, and the articles don't specify how much blood flow contributes or exactly why the tingling happens.

On the funny bone — the article describes it as "an impact on the comparatively unprotected ulnar nerve near the elbow" that causes "the briefest electric shock type of paresthesia." So it's the same mechanism (nerve getting hit), but it's instantaneous impact rather than sustained pressure, and it's acute and sharp rather than the gradual build-up and relief you experienced. Same nerve-based paresthesia, different trigger.