As someone who has recently had terrible back and leg pain from sciatica compounded with arthritis in the knee so that it was very painful to move and hard to sleep with the pain once woken in the night, it does make you think is this what it is going to be like from now until until you die.
As one gets older death moves more to the forefront off your mind as the inevitable end to your life. For atheists like myself there is no fantasy life ever lasting, just eternal non existence. So what to do, well as many have said before me, just focus on living and enjoy the moments you can, enjoy your friends and family , appreciate the world in all its beauty and magnificence and appreciate the love, care and tenderness that people and the natural world can show, hopefully balancing the nasty brutality of the hierarchic, greedy world and its leaders.
2 mottos I have regularly returned to as I grow older are '' enjoy today because tomorrow might be slightly worse' and enjoy life now while you can' and try to make life better for others. Remember that while there are problems with ageing but it is better than the alternative.