I have a friend. He was a huge talmid chochom and masmid. He was always learning and wrote many sefarim. He loved to teach and to speak. He would daven and daven and daven - last guy in shul. He has a very large family. He is not an old man but his body is wracked with disease and he is a shell of the man he once was - vibrant, alive, filled with simcha and enthusiasm. Now he can barely walk or talk.
To see him is to be heartbroken.
1] Take advantage of you health if you have it. It doesn't last forever. Do lots of mitzvos and thank Hashem with every breath.
2] We aren't in chage of ANYTHING. As long as Hashem gives it we have it - the moment He deems fit to take it away it is GONE.
3] Complain less about your tzaros. They could be much worse.
4] Always remember that no matter how much success you have in this world - at that very moment many people are suffering.
5] At the end all that really matters is the good that you did with your life. Try to do thing about which people will talk glowingly and be inspired by after you go. I have never heard anyone say at a shiva home: "Moish was so special. He could down 3 hefty portions of spaghetti and meatballs and still have planty of room for dessert". Or "Yocheved loved fancy hotels. She must have spent a third of her life in them".