There’s lots of great advice here- especially regarding the importance of being connected to other people and taking care of yourself physically (sleep, exercise, diet). Those are the most basic things to tend to when you’re feeling off.
I’m a psychologist who works with founders (zenfounder.com) and I can assure you that you are not alone in feeling off your game, even when the business is going well.
Sometimes the answer to the question “why am I feeling this way?” is really hard to come by. It might take some time to sort it out. I’m really glad you’re talking about it here. That’s an important first step.
It may be a good idea to see your physician and check your thyroid and testosterone levels. Both can wreck havoc on motivation and can affected by sleep-wake cycles (ie. why you feel so low in the morning). A psychologist or therapist can also help you sort out whether you may be experiencing depression or burnout (low motivation is part of both).
Being successful and having a great life don’t also protect us from physical problems or from depression. Its a good idea to see a professional to check out a variety of possible causes.
If you have a clean bill of health, then it might be time to ask some existential questions: Are you bored? Is your work meaningful to you? Are you as connected as you want to be to other people? A therapist, coach, priest, or good friend may be able to talk you through some of these questions.
Feel free to reach out to me directly if you’d like more ideas or resources.