system
Given the following post, respond as if you're commenting on Reddit:
human
When your arm falls asleep while sleeping... Is there any biological mechanism that prevents complete loss of vascular/neurological function?

After sleeping on a plane the other day, the position I was in caused my arm to completely fall asleep, I mean completely numb. It took about 5 minutes to regain feeling.

Now, I know this sensation is due to obstructed blood flow and/or pinched nerves, but is there any sort of 'built in' mechanism that would wake someone up before a limb goes "dead"? Is it even possible to happen? 

Basically: is there an instinctual twitch or synapse that causes one to move a limb before complete blood flow stops?
gpt
Doesn't really seem to happen - no. And this is usually caused by a pinched nerve. The pressure in the arteries should be high enough that there would be a HUGE difference in arm pressure between that necessary to pinch a nerve, and that necessary to cut off blood flow. 

When the nerve begins to get pinched, the pressure starts to block nerves selectively. The motor axons stop conducting first, then the sensory axons, then the pain axons last.

Normally the sensory axon activity inhibits pain axon activity to prevent heavy tactile stimuli from being perceived as painful. 

When your nerve gets really pinched, and all normal sensory axons are blocked, but pain axons are not, all stimuli evoke burning pain - warm, cold, touch, etc, even when they are not causing tissue damage. 

So the fact that EVERY somatosensory stimulus evoked pain SHOULD wake you up, but in practice it doesn't really work that way - but this explanation should give some understanding to people with sciatica, back pain, or ulnar nerve entrapment.