I get it. What you are expressing. It is also my experience. Fortunately it is not consistent. comes and goes. My realizations from it are that there is a basic underlying question that is not being answered, "What for? What is the purpose of it all? I will die so why bother to do anything? Isn't there something else? Where is it? What is it?" A friend has written a book dealing with the issue. Which is interestingly enough addressed in Ecclesiastics by King Solomon, I believe. He had everything. But what was the purpose of it all? What's the use? My friend's book is titled," Vanity Karma"... vanity in this instance refers to "in vain" https://vanitykarma.com/ I think people who are in prison for a long sentence, maybe life, may have this feeling. My personal conclusion and that which gets me by, is that I am in prison. My challenge is to be released. I am always seeking that knowledge which will set me free. So that has become my purpose. So now I have found purpose. Problem solved. Wishing you well and a successful journey...