You'll want to give the doctor a sense of what's going on with you (just like you've done here), and then to help them find any medical issues that may be causing your problems. So give an overall description of the problem and how serious it is (sort of like in your initial post - your lack of energy, inability to do things, and lots of related problems) - including some examples or specifics (like these) can help make that clearer. And be sure to describe anything that seems like it could be physiological (the three that stuck out to me were lack of energy, difficulty focusing, and anxiety / panic attacks - you might be able to think of some others).

The doctor will have questions which will help guide the conversation, and you can always ask whether they want more details about something. Do you think that figuring out what to say to the doctor could be a barrier for you? If so, let me know - I could say more about it.