Are you talking about a numb feeling? Because a pinched nerve, or poor blood circulation typically cause numb sensations and tingling sensations. Are your hands and feet cold? Or sometimes it can start in just your fingers and toes. Are they turning pale or slightly blue/purple?
I always worry about getting blood clots or having poor circulation; even before I wasn't so much of a hypochondriac, problems related to blood would always concern me. I do sometimes feel like I am getting poor circulation in my legs (it just feels weird and tingly) - and the more I start to think about it, the worse it can become.