Every drive has the occasional defects in manufacturing. These defects prevent reading/writing to a sector. As a way to combat this, the sectors that are flagged as damaged are moved, or reallocated.
As every drive series is different, sector reallocation is a poor indicator of drive health. Some large drives don't have enough data (user submitted records of "good" drive information), so they default to the danger readings of much smaller drives.
In short, you should worry if reallocated sectors is increasing consistently. If the number is constant after several boots, then it isn't a problem. If it increases consistently then you should be worried.
You haven't seen anything until you've seen this.
Wow! I didn't know the blue screen of death could get a blue screen of death.