Why do we get ‘pins and neddles’ if we lean on a part of our body for too long, or if we sit down for too long?

Question: Why do we get 'pins and neddles' if we lean on a part of our body for too long, or if we sit down for too long?
- Keywords:
  blood,
  body,
  human
Asked by to Daren, Lynne, Phillip, Simon on 21 Jun 2014. This question was also asked by .
- anon answered on 21 Jun 2014:
  
  Pins and needles happen when you cut off the blood supply to a certain part of your body. Your nerves can’t work as well with less blood so they send warning signals to your brain so that you know to move and restore the blood supply. Pins and needles can be thought of your body’s low-blood alarm!

Question: Why do we get 'pins and neddles' if we lean on a part of our body for too long, or if we sit down for too long?