Changes in energy level might be the best way to characterize bipolar disorder in a sufferer. Also called manic-depressive illness, the condition takes you to two extremes of the same bleak rainbow. On the one side, all the excitement that you are feeling when manic causes you to be bustling and beside yourself; and on the other side of the same coin, your sadness can leave you powerless beyond understanding. This is not too difficult to observe, but it might take some patience to witness it all. You need to take note of this by all means.
Depression changes one's energy level, and so does excitement, whether or not the impulses are pointless. Sometimes bipolar disorder might be difficult to tell in a person because when they are depressed they could feel restless and agitated the same as when they suffer from mania.
So, all the fidgety movements and pacing could point in either direction, and unless you have more information you might not be able to conclude that it is bipolar disorder that they suffer from.
Most folks feel sluggish and inactive when they are depressed, and they characterize their obsession or mania with extensive activity, which does not seem to head in any direction. That's when they suffer from manic-depressive infirmity. If you are a very observant person, you might be able to observe these changes in their persons before too long so that you can get them help; the sufferer is not likely to be able to notice it themselves.