Sometimes when I sit just right all the feeling goes away in my arms, legs, back, hands, and feet. Can this be a pinched nerve?

Yes. A compression of the nerves or spinal cord inthe neck can lead to numbness and weakness in the arms and legs. Since permanent nerve damage or even paralysis can develop an examination by a spine surgeon and and MRI of the spine is needed.
Concerning. Yes it could be a pinched nerve (or even more concerning impingement of the spinal cord). This needs to be evaluated now!