numbness/tingling when laying down

  When I try to sleep at night and I lay on my side I get a numbing and tingling sensation on the side I am not on.  It can be very painful.  It does ease up if I change positions.  Sometimes it happens very quickly and other times it takes some time.  I am not a good sleeper and this pain has not helped.  I am overweight and am working on this and sleeping on my back prohibits any kind of sleep.  Any suggestions as to what might be causing this?
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The most likely problem here is that your problem is in some way posture
related, if the tingling involves both arms and legs ( you did not specify )
the most likely location of the problem would be in the neck.
If this is the case the posture you adopt may cause pressure on the
cervical spinal cord producing your symptoms.
I would suggest that you need to have your cervical spine investigated ,
by means of a neurological examination and whatever tests are
indicated after that point.
If this is related to neck posture, a simple change in posture or wearing a collar
might be sufficient. The first step needs to be the establishemnt of a
diagnosis and this will require a visit to a physician.