Moving a MBP shouldn't shut it down, or put it to sleep, or anything like that.
The sudden motion sensors, should park the hard drive head to prevent damage to the disk, but that's it. I can move mine around fine no problem.
Try looking at the console to see if there's any indication of what's causing it. My Dad's iMac was going to sleep randomly and the console told me it was overheating, and I found the vents clogged with dust. I'm not sure what you should search for though, try 'sleep' or 'shut', 'shut down' etc and see if anything comes up.