[darkleeroy]

A sick period is the time a cigar takes to settle down and allow the flavor to mature. During this period, cigars are characteristically dull. For the most part sick periods only apply to Cuban cigars, because the leaves aren't usually aged at all before being used to roll. This is due to the high demand of Cuban cigars in general but can also apply to cigars that are green (read:fresh) coming off the table.

Likewise, it is more of a trial and error process, and listening to the opinions of others that help determine what a sick period would be. If you browse the island (that one) reviews, you'll see that people also tend to put the date or box codes of their cigars in the reviews for that purpose.

As for non-Cuban cigars, most of the leaves are aged a couple of years before being rolled and shipped. As a result, these cigars don't really experience a sick period, and are usually good to smoke right off the shelf. At the same time, you can still age non-cubans, and there are some that will continue to improve. But like I said earlier, it's all trial and error.