Sounds like it is over heating and the movement is causing the heatsink to move and not work properly. I assume the fan still works. I suggest the following:
First, use a can of compressed air to blow out the intake and exhaust vents on your system.
Then disassemble the system and remove the heatsink/fan assembly. Thoroughly clean the CPU and the backside of the heatsink and then apply new thermal compound and then firmly attach the heatsink/fan assembly. While inside the system, use you can of air to blow out any dust that you can.
Regardless, what make and model of laptop are you using?