Small blood vessels can narrow in response to cold, temporarily reducing blood flow to a finger. Sleeping in an awkward position may also restrict circulation or compress nerves, causing numbness. Another possible explanation is Raynaud’s phenomenon, which can turn fingers white or blue, then red as circulation returns. Many episodes pass, but appearance alone cannot establish the cause. An unexplained change is worth taking seriously, even if it eventually resolves and your hand feels normal again.
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