I too have this "core of your being" exhaustion. In some other conversation here in the Mayo LC forum, someone mentioned the Huberman Lab podcasts. I started listening to some of them, and one in particular gave me new information about how light can affect our sleep. Huberman recommended going outside and getting early morning light to set the stage for how your body will set its circadian rhythm that day. I really do think it is helping me. My sleep and fatigue has gotten better. Huberman also talks about red light exposure and I have started doing that, both by going outside at optimal times and by going to a business that offers it. I can't believe that I consulted with the top sleep specialist at a university medical center, and she offered me plenty of sleeping pills, did at-home and in-lab sleep studies looking for apnea and whatever, told me about sleep hygiene and gave me an online course to take, but she NEVER mentioned the importance of early morning light. It's so simple, and when you think about it, it is the reason we get jet lag when we travel. Thanks to the info we get in this forum!