Sake contains little or no sulfites, making morning a much more appealing concept as you will have either very little or no hangover. Some claim that this is merely a myth. I think it generally coincides with the quality of the sake. The better the sake, the less the hangover. Sake is a grain alcohol, brewed very much like beer.
Fresh sake is always best.
That bottle you've never opened but thought you would get around to sometime is probably best left on the shelf for decoration. The word sake does not always mean Japanese rice wine. It can also be used for alcoholic beverages in general. Also sakana does not always imply fish. It can also mean a side dish, thus the phrase sake no sakana .