I can't say why you feel this way, I can only share my experience and hope it may resonate. I used to feel this way often. For me, it meant I needed more enjoyable things in my life and connection to people I appreciate and love. I added more of both in my life, as I could and over time, and now I don't have these feelings the day after something nice.
Maybe it is a positive sign to add more good things, people and experiences into your life?