CPU at 100%, but no processes showing significant usage Situation:

All 4 cores maxed out. Mac noticeably lagging.

Attempted Solution:

(Reveals wildly contradictory information.)


Closed all applications
Opened Activity Monitor
Totaled all Process ID activity and noticed that all processes listed (including activity monitor and finder) only add up to about 10-20% CPU usage, BUT ALL 4 CORES ARE STILL REDLINED/MAXED OUT.


Additional Info:

Activity monitor also says that:


User Usage is &lt; 5%
System Usage is almost steady at 85% (yet no PID's show significant CPU use)
Idle 10%


The system in question is running OS X 10.7.5 (Lion).
(I'm writing from another machine.)

Three Part Question:


HOW CAN WE STOP THIS BEHAVIOR?
Why is the total CPU usage drastically different from the PID list total?
(BONUS) Why isn't there any system PID showing up that correlates with the 85% system usage?
NOTE: This is only a partial answer, so any other info as to why this happened could be good for others with this problem.

Literally, upon simply plugging in the power cord, all symptoms immediately stopped. (Battery was well above 10%.)


CPU usage dropped to normal levels. 
Resulting sluggishness stopped as well.