The symptoms
you are describing could be related to a blood flow problem or more likely an
issue with neuropathy (a disease of the nerves). This can be due to spinal disease, in your
case potentially in the upper spine, or cervical area, where the nerves
originate. This may be exacerbated by
certain positions, which put extra pressure on those areas.
You might start by talking to a neurologist
for more information.