Unless you are a yogi like Milarepa you should definitely plan and prepare as if you are going to live another 50 or 70 years or whatever; you should plan that way. But in you, you really should know that that might not be the case. And not only that, we should not only think of our impermanence, but also everything else. Any kind of situation, you name it, everything is impermanent. That way it is about everything.
So how do we handle this? I say take a deep breath and take it easy. The most important thing is to do your best with every moment of your life. Be good, sincere, kind, honest and hard working. If you are meditating, meditate well, if you are doing something, do it well. Do your best in every moment. That is how to take care of the understanding of impermanence. If you just sit there and worry that you might die in the next hour, that’s not the best use of the understanding of impermanence. Make the best out of your lives, even if you are going to die in the next hour you will not have any regret if you have done your best. That is how to handle it.
From “Essential Teachings of Gampopa”