co-written by Rick Olazabal, BSc, ND
Your body has the wonderful ability to perceive its position in space. This is known as “proprioception” (proprio- = self, -ception = awareness). It does so by an intricate network of receptors and their association nerve signals that transmit stimuli (i.e. information) with regards to pressure, stretch, vibration, acceleration, etc.
This is part of the reason when you’ve been sitting (or standing) in a specific position for a too long period of time it begins to get uncomfortable and you need to move.
Your body is telling you to move.
This serves as an early warning system, so that body parts aren’t damaged due too much pressure, which can lead to decreased blood flow, and reduced nerve signalling. When you don’t move or reposition yourself that body part begins to feel numb (“falls asleep”), followed by the rather weird sensation of pins-and-needles (i.e. “paraesthesia”) once nerve signals and blood flow resume.
Why our arms, feet or legs fall asleep?
When the body part becomes compressed, the pressure interferes with nerve signalling and blood flow in that area. Think of the blood flow as water in a hose, but the hose is now knotted—pressure builds up, but no water comes out. Similarly, think of nerve signalling as an electrical wire that has been interrupted. If there is no signal being sent to your brain, then the brain cannot perceive what is going on, and hence the loss of sensation. If the blood obstruction goes for long enough (e.g. hours), then this can cause tissue and nerve damage.
When it occurs?
Normally, this happens when pressure is applied to that part of the body or somewhere higher up. For example, if your hand feels numb or cold you may be leaning too hard on your forearm or elbow. Similarly, if your leg falls asleep, you may be sitting on a hard surface, or in such a position that it is interfering with the nerve signalling—namely, the sciatic nerve and its branches—for that leg.
Mainly during our sleep?
Proprioception isn’t necessarily affected by sleep. As a matter of fact, you would turn and readjust your position in bed throughout the night, as you cycle through the stages of sleep. However, there are times when sleep becomes so heavy that you just don’t move. This is typical of excess alcohol consumption, and of some medication (e.g. hypnotics).
Is there an underlying health condition?
For the vast majority of people, an arm or a leg “falling asleep” isn’t a major health concern. However, during a regular check-up, your primary care provider will assess any risk factors. People with—or at a risk of developing—diabetes, thyroid condition, neurological and/or circulatory problems should ensure active monitoring. Other conditions that can lead to similar sensation (or lack thereof) and paraesthesia include :
- Vitamin B12 deficiency,
- Raynaud’s syndrome (due to cold weather and anxiety),
- Carpal tunnel syndrome,
- Cervical spondylosis.
When in doubt, check with your physician, licensed naturopathic doctor, and/or chiropractor.
What can be done?
Move, move, move! Exercise improves circulation and keeps you healthy and less stressed! You don’t need much, just as little as 30 mins a day of just walking works wonders! Limit your alcohol consumption, especially before bed. And, of course, as with everything else, eat meals rich in minerals and vitamins!